An acronym is a word 06 or name formed from the initial components of a longer name or phrase. Acronyms are usually formed from the initial letters of words, as in NATO 06 (North Atlantic Treaty Organization), but sometimes use syllables, as in Benelux (short for Belgium, the Netherlands, and Luxembourg). They can also be a mixture, as in radar (RAdio Detection And Ranging).
The broader sense of acronym—the meaning of which includes terms pronounced as letters—is sometimes criticized, but it is the term's original meaning and is in common use. Dictionary and style-guide editors are not in universal agreement on the naming for such abbreviations, and it is a matter of some dispute whether the term acronym can be legitimately applied to abbreviations which are not pronounced "as words", nor do these language authorities agree on the correct use of spacing, casing, and punctuation.
Abbreviations formed from a string of initials and usually pronounced as individual letters are sometimes more specifically called initialisms or alphabetisms; examples are FBI from Federal Bureau of Investigation, and e.g. from Latin exempli gratia.
The word acronym is formed from the Greek roots acr-, meaning "height, summit, or tip" and -onym, meaning "name". This neoclassical compound appears to have originated in German, with attestations for the German form Akronym appearing as early as 1921. Citations in English date to a 1940 translation of a novel by the German writer Lion Feuchtwanger.
Whereas an abbreviation may be any type of shortened form, such as words with the middle omitted (for example, Rd for Road or Dr for Doctor) or the end truncated (as in Prof. for Professor), an acronym is—in the broad sense—formed from the first letter or first few letters of each important word in a phrase (such as AIDS, from acquired immuno-deficiency syndrome, and scuba from self-contained underwater breathing apparatus). However, this is only a loose rule of thumb, as some acronyms are built in part from the first letters of morphemes (word components; as in the i and d in immuno-deficiency) or using a letter from the middle or end of a word, or from only a few key words in a long phrase or name. Less significant words such as in, of, and the are usually dropped (NYT for The New York Times, DMV for Department of Motor Vehicles), but not always (TICA for The International Cat Association, DoJ for Department of Justice).
Abbreviations formed from a string of initials and usually pronounced as individual letters (as in FBI from Federal Bureau of Investigation, and e.g. from Latin exempli gratia) are sometimes more specifically called initialisms or alphabetisms. Occasionally, some letter other than the first is chosen, most often when the pronunciation of the name of the letter coincides with the pronunciation of the beginning of the word (example: BX from base exchange). Acronyms that are usually pronounced as words, such as AIDS and scuba, are sometimes called word acronyms, to disambiguate them more clearly from initialisms, especially since some users of the term "initialism" use "acronym" in a narrow sense meaning only the type sounded out as letters. Another sub-type of acronym (or a related form, depending upon one's definitions) is the syllabic abbreviation, which is composed specifically of multi-letter syllabic (even multi-syllabic) fragments of the abbreviated words; some examples are FOREX from foreign exchange, and Interpol from international + police, though its full proper name in English is the International Criminal Police Organization). Usually the first syllable (or two) is used from each major component word, but there are exceptions, such as the US Navy term DESRON or DesRon from destroyer squadron.
There is no special term for abbreviations whose pronunciation involves the combination of letter names with words, or with word-like pronunciations of strings of letters, such as JPEG (/ˈdʒeɪpɛɡ/) and MS-DOS (/ˌɛmɛsˈdɒs/). Similarly, there is no unique name for those that are a mixture of syllabic abbreviations and initialisms; these are usually pronounced as words (e.g., radar from radio detection and ranging, consisting of one syllabic abbreviation and three single letters, and sonar from sound navigation ranging, consisting of two syllabic abbreviations followed by a single acronymic letter for ranging); these would generally qualify as word acronyms among those who use that term. There is also some disagreement as to what to call an abbreviation that some speakers pronounce as letters but others pronounce as a word. For example, the terms URL and IRA (for individual retirement account) can be pronounced as individual letters: /ˌjuːˌɑːrˈɛl/ and /ˌaɪˌɑːrˈeɪ/, respectively; or as a single word: /ɜːrl/ and /ˈaɪrə/, respectively. The same character string may be pronounced differently when the meaning is different; IRA is always sounded out as I-R-A when standing for Irish Republican Army.
The spelled-out form of an acronym, initialism, or syllabic abbreviation (that is, what that abbreviation stands for) is called its expansion.
Lexicography and style guides
It is an unsettled question in English lexicography and style guides whether it is legitimate to use the word acronym to describe forms that use initials but are not pronounced as a word. While there is plenty of evidence that acronym is used widely in this way, some sources do not acknowledge this usage, reserving the term acronym only for forms pronounced as a word, and using initialism or abbreviation for those that are not. Some sources acknowledge the usage, but vary in whether they criticize or forbid it, allow it without comment, or explicitly advocate for it.
Some mainstream English dictionaries from across the English-speaking world affirm a sense of acronym which does not require being pronounced as a word. American English dictionaries such as Merriam-Webster, Dictionary.com's Random House Webster's Unabridged Dictionary and the American Heritage Dictionary as well as the British Oxford English Dictionary and the Australian Macquarie Dictionary all include a sense in their entries for acronym equating it with initialism, although The American Heritage Dictionary criticizes it with the label "usage problem". However, many English language dictionaries, such as the Collins COBUILD Advanced Dictionary, Cambridge Advanced Learner's Dictionary, Macmillan Dictionary, Longman Dictionary of Contemporary English, New Oxford American Dictionary, Webster's New World Dictionary, and Lexico from Oxford University Press do not acknowledge such a sense.
Most of the dictionary entries and style guide recommendations regarding the term acronym through the twentieth century did not explicitly acknowledge or support the expansive sense. The Merriam–Webster's Dictionary of English Usage from 1994 is one of the earliest publications to advocate for the expansive sense, and all the major dictionary editions that include a sense of acronym equating it with initialism were first published in the twenty-first century. The trend among dictionary editors appears to be towards including a sense defining acronym as initialism: The Merriam-Webster Collegiate Dictionary added such a sense in its eleventh edition in 2003, and both the Oxford English Dictionary and the American Heritage Dictionary added such senses in their 2011 editions. The 1989 edition of the Oxford English Dictionary only included the exclusive sense for acronym and its earliest citation was from 1943. In early December 2010, Duke University researcher Stephen Goranson published a citation for acronym to the American Dialect Society e-mail discussion list which refers to PGN being pronounced "pee-gee-enn," antedating English language usage of the word to 1940. Linguist Ben Zimmer then mentioned this citation in his December 16, 2010 "On Language" column about acronyms in The New York Times Magazine. By 2011, the publication of the third edition of the Oxford English Dictionary added the expansive sense to its entry for acronym and included the 1940 citation. As the Oxford English Dictionary structures the senses in order of chronological development, it now gives the "initialism" sense first.
English language usage and style guides which have entries for acronym generally criticize the usage that refers to forms that are not pronounceable words. Fowler's Dictionary of Modern English Usage says that acronym "denotes abbreviations formed from initial letters of other words and pronounced as a single word, such as NATO (as distinct from B-B-C)" but adds later "In everyday use, acronym is often applied to abbreviations that are technically initialisms, since they are pronounced as separate letters." The Chicago Manual of Style acknowledges the complexity ("Furthermore, an acronym and initialism are occasionally combined (JPEG), and the line between initialism and acronym is not always clear") but still defines the terms as mutually exclusive. Other guides outright deny any legitimacy to the usage: Bryson's Dictionary of Troublesome Words says "Abbreviations that are not pronounced as words (IBM, ABC, NFL) are not acronyms; they are just abbreviations." Garner's Modern American Usage says "An acronym is made from the first letters or parts of a compound term. It's read or spoken as a single word, not letter by letter." The New York Times Manual of Style and Usage says "Unless pronounced as a word, an abbreviation is not an acronym."
In contrast, some style guides do support it, whether explicitly or implicitly. The 1994 edition of Merriam-Webster's Dictionary of English Usage defends the usage on the basis of a claim that dictionaries do not make a distinction. The BuzzFeed style guide describes CBS and PBS as "acronyms ending in S".
Comparing a few examples of each type
- Pronounced as a word, containing only initial letters
- Pronounced as a word, containing a mixture of initial and non-initial letters
- Pronounced as a combination of spelling out and a word
- Pronounced only as a string of letters
- Pronounced as a string of letters, but with a shortcut
- IEEE: (I triple-E) "Institute of Electrical and Electronics Engineers"
- NAACP: (N double-A C P or N A A C P) "National Association for the Advancement of Colored People"
- NCAA: (N C double-A or N C two-A or N C A A) "National Collegiate Athletic Association"
- Shortcut incorporated into name
- 3M: (three M) originally "Minnesota Mining and Manufacturing Company"
- (ISC)²: (ISC squared) "International Information Systems Security Certification Consortium"
- W3C: (W-three C) "World Wide Web Consortium"
- A2DP: (A-two D P) "Advanced Audio Distribution Profile"
- C4ISTAR: (C-four Istar) "Command, Control, Communications, Computers, Intelligence, Surveillance, Target Acquisition, and Reconnaissance"
- E3: (E-three) "Electronic Entertainment Expo"
- Mnemonic acronyms, an abbreviation that is used to remember phrases or principles
- KISS (Kiss) "Keep it simple, stupid", a design principle preferring simplicity
- SMART (Smart) "Specific, Measurable, Assignable, Realistic, Time-related", A principle of setting of goals and objectives
- FAST (Fast) "Facial drooping, Arm weakness, Speech difficulties, Time", helps detect and enhance responsiveness to the needs of a person having a stroke
- DRY (Dry) "Don't repeat yourself", A principle of software development aimed at reducing repetition of software patterns
- SAMPLE (Sample) "Signs/Symptoms, Allergies, Medications, Past Pertinent medical history, Last Oral Intake, Events Leading Up To Present Illness", to remember key questions for a person's medical assessment
- Multi-layered acronyms
- AIM: "AOL Instant Messenger," in which "AOL" originally stood for "America Online"
- AFTA: "ASEAN Free Trade Area," where ASEAN stands for "Association of Southeast Asian Nations"
- NAC Breda: (Dutch football club) "NOAD ADVENDO Combinatie" ("NOAD ADVENDO Combination"), formed by the 1912 merger of two clubs from Breda:
- GIMP: "GNU image manipulation program"
- VHDL: "VHSIC hardware description language," where "VHSIC" stands for "Very High Speed Integrated Circuit" (a U.S. government program)
- Recursive acronyms, in which the abbreviation refers to itself
- Pseudo-acronyms, which consist of a sequence of characters that, when pronounced as intended, invoke other, longer words with less typing This makes them gramograms.
- CQ: cee-cue for "seek you", a code used by radio operators
- IOU: i-o-u for "I owe you"
- K9: kay-nine for "canine," used to designate police units utilizing dogs
- Abbreviations whose last abbreviated word is often redundantly included anyway
- Pronounced as a word, containing letters as a word in itself
- PAYGO: "pay-as-you-go"
Historical and current use
Acronymy, like retronymy, is a linguistic process that has existed throughout history but for which there was little to no naming, conscious attention, or systematic analysis until relatively recent times. Like retronymy, it became much more common in the 20th century than it had formerly been.
Ancient examples of acronymy (regardless of whether there was metalanguage at the time to describe it) include the following:
- Acronyms were used in Rome before the Christian era. For example, the official name for the Roman Empire, and the Republic before it, was abbreviated as SPQR (Senatus Populusque Romanus). Inscriptions dating from antiquity, both on stone and on coins, use many abbreviations and acronyms to save space and work. For example, Roman first names, of which there was only a small set, were almost always abbreviated. Common terms were abbreviated too, such as writing just "F" for filius, meaning "son", a very common part of memorial inscriptions mentioning people. Grammatical markers were abbreviated or left out entirely if they could be inferred from the rest of the text.
- So-called nomina sacra (sacred names) were used in many Greek biblical manuscripts. The common words "God" (Θεός), "Jesus" (Ιησούς), "Christ" (Χριστός), and some others, would be abbreviated by their first and last letters, marked with an overline. This was just one of many kinds of conventional scribal abbreviation, used to reduce the time-consuming workload of the scribe and save on valuable writing materials. The same convention is still commonly used in the inscriptions on religious icons and the stamps used to mark the eucharistic bread in Eastern Churches.
- The early Christians in Rome, most of whom were Greek rather than Latin speakers, used the image of a fish as a symbol for Jesus in part because of an acronym: "fish" in Greek is ichthys (ΙΧΘΥΣ), which was said to stand for Ἰησοῦς Χριστός Θεοῦ Υἱός Σωτήρ (Iesous Christos Theou huios Soter: "Jesus Christ, God's Son, Savior"). This interpretation dates from the 2nd and 3rd centuries and is preserved in the catacombs of Rome. And for centuries, the Church has used the inscription INRI over the crucifix, which stands for the Latin Iesus Nazarenus Rex Iudaeorum ("Jesus the Nazarene, King of the Jews").
- The Hebrew language has a long history of formation of acronyms pronounced as words, stretching back many centuries. The Hebrew Bible ("Old Testament") is known as "Tanakh", an acronym composed from the Hebrew initial letters of its three major sections: "Torah" (five books of Moses), "Nevi'im" (prophets), and "K'tuvim" (writings). Many rabbinical figures from the Middle Ages onward are referred to in rabbinical literature by their pronounced acronyms, such as Rambam and Rashi from the initial letters of their full Hebrew names: "Rabbi Moshe ben Maimon" and "Rabbi Shlomo Yitzkhaki".
During the mid- to late 19th century, an acronym-disseminating trend spread through the American and European business communities: abbreviating corporation names, such as on the sides of railroad cars (e.g., "Richmond, Fredericksburg and Potomac Railroad" → "RF&P"); on the sides of barrels and crates; and on ticker tape and in the small-print newspaper stock listings that got their data from it (e.g. American Telephone and Telegraph Company → AT&T). Some well-known commercial examples dating from the 1890s through 1920s include "Nabisco" ("National Biscuit Company"), "Esso" (from "S.O.", from "Standard Oil"), and "Sunoco" ("Sun Oil Company").
Another driver for the adoption of acronyms was modern warfare, with its many highly technical terms. While there is no recorded use of military acronyms in documents dating from the American Civil War (acronyms such as "ANV" for "Army of Northern Virginia" postdate the war itself), they had become somewhat common in World War I and were very much a part even of the vernacular language of the soldiers during World War II, who themselves were referred to as G.I.s.
The widespread, frequent use of acronyms across the whole range of registers is a relatively new linguistic phenomenon in most languages, becoming increasingly evident since the mid-20th century. As literacy rates rose, and as advances in science and technology brought with them a constant stream of new (and sometimes more complex) terms and concepts, the practice of abbreviating terms became increasingly convenient. The Oxford English Dictionary (OED) records the first printed use of the word initialism as occurring in 1899, but it did not come into general use until 1965, well after acronym had become common.
In English, acronyms pronounced as words may be a 20th-century phenomenon. Linguist David Wilton in Word Myths: Debunking Linguistic Urban Legends claims that "forming words from acronyms is a distinctly twentieth- (and now twenty-first-) century phenomenon. There is only one known pre-twentieth-century [English] word with an acronymic origin and it was in vogue for only a short time in 1886. The word is colinderies or colinda, an acronym for the Colonial and Indian Exposition held in London in that year." However, although acronymic words seem not to have been employed in general vocabulary before the 20th century (as Wilton points out), the concept of their formation is treated as effortlessly understood (and evidently not novel) in an Edgar Allan Poe story of the 1830s, "How to Write a Blackwood Article", which includes the contrived acronym "P.R.E.T.T.Y.B.L.U.E.B.A.T.C.H."
Early examples in English
The use of Latin and Neo-Latin terms in vernaculars has been pan-European and predates modern English. Some examples of acronyms in this class are:
- A.M. (from Latin ante meridiem, "before noon") and P.M. (from Latin post meridiem, "after noon")
- A.D. (from Latin Anno Domini, "in the year of our Lord"), whose complement in English, B.C. [Before Christ], is English-sourced
- O.K., a term of disputed origin, dating back at least to the early 19th century, now used around the world
The earliest example of a word derived from an acronym listed by the OED is "abjud" (now "abjad"), formed from the original first four letters of the Arabic alphabet in the late 18th century. Some acrostics predate this, however, such as the Restoration witticism arranging the names of some members of Charles II's Committee for Foreign Affairs to produce the "CABAL" ministry.
Acronyms are used most often to abbreviate names of organizations and long or frequently referenced terms. The armed forces and government agencies frequently employ acronyms; some well-known examples from the United States are among the "alphabet agencies" (also jokingly referred to as "alphabet soup") created by Franklin D. Roosevelt (also of course known as "FDR") under the New Deal. Business and industry also are prolific coiners of acronyms. The rapid advance of science and technology in recent centuries seems to be an underlying force driving the usage, as new inventions and concepts with multiword names create a demand for shorter, more manageable names. One representative example, from the U.S. Navy, is "COMCRUDESPAC", which stands for "commander, cruisers destroyers Pacific"; it is also seen as "ComCruDesPac". "YABA-compatible" (where "YABA" stands for "yet another bloody acronym") is used to mean that a term's acronym can be pronounced but is not an offensive word, e.g. "When choosing a new name, be sure it is 'YABA-compatible'."
Acronym use has been further popularized by text messaging on mobile phones with short message service (SMS), and instant messenger (IM). To fit messages into the 160-character SMS limit, and to save time, acronyms such as "GF" ("girlfriend"), "LOL" ("laughing out loud"), and "DL" ("download" or "down low") have become popular. Some prescriptivists disdain texting acronyms and abbreviations as decreasing clarity, or as failure to use "pure" or "proper" English. Others point out that language change has happened for thousands of years, and argue that it should be embraced as inevitable, or as innovation that adapts the language to changing circumstances. In this view, the modern practice is just as legitimate as those in "proper" English of the current generation of speakers, such as the abbreviation of corporation names in places with limited writing space (e.g., ticker tape, newspaper column inches).
Exact pronunciation of "word acronyms" (those pronounced as words rather than sounded out as individual letters) often vary by speaker population. These may be regional, occupational, or generational differences, or simply a matter of personal preference. For instance, there have been decades of online debate about how to pronounce GIF (/ɡɪf/ or /dʒɪf/) and BIOS (/ˈbaɪoʊs/, /ˈbaɪoʊz/, or /ˈbaɪɒs/). Similarly, some letter-by-letter initialisms may become word acronyms over time, especially in combining forms; IP for Internet Protocol is generally said as two letters, but IPsec for Internet Protocol Security may be pronounced as /ˌaɪˈpiːsɛk/ or /ˈɪpsɛk/, with the latter increasing over time (along with variant spellings like "IPSEC" and "Ipsec"). Pronunciation may even vary within a single speaker's vocabulary, depending on narrow contexts. As an example, the database programming language SQL is said as three letters in most cases, but in reference to Microsoft's implementation is traditionally pronounced the same as the word sequel.
Expansion on first use
In formal writing for a broad audience, the expansion is typically given at the first occurrence of the acronym within a given text, for the benefit of those readers who do not know what it stands for.
In addition to expansion at first use, some publications also have a key listing all the acronyms used and what their expansions are. This is a convenience for readers for two reasons. The first is that if they are not reading the entire publication sequentially (which is a common mode of reading), then they may encounter an acronym without having seen its expansion. Having a key at the start or end of the publication obviates skimming over the text searching for an earlier use to find the expansion. (This is especially important in the print medium, where no search utility is available.) The second reason for the key feature is its pedagogical value in educational works such as textbooks. It gives students a way to review the meanings of the acronyms introduced in a chapter after they have done the line-by-line reading, and also a way to quiz themselves on the meanings (by covering up the expansion column and recalling the expansions from memory, then checking their answers by uncovering). In addition, this feature enables readers possessing knowledge of the abbreviations not to have to encounter expansions (redundant for such readers).
Expansion at first use and the abbreviation-key feature are aids to the reader that originated in the print era, but they are equally useful in print and online. The online medium also allows more aids, such as tooltips, hyperlinks, and rapid search via search engine technology.
Acronyms often occur in jargon. An acronym may have different meanings in different areas of industry, writing, and scholarship. The general reason for this is convenience and succinctness for specialists, although it has led some to obfuscate the meaning either intentionally, to deter those without such domain-specific knowledge, or unintentionally, by creating an acronym that already existed.
The medical literature has been struggling to control the proliferation of acronyms as their use has evolved from aiding communication to hindering it. This has become such a problem that it is even evaluated at the level of medical academies such as the American Academy of Dermatology. 
Acronyms are often taught as mnemonic devices, for example in physics the colors of the visible spectrum are said to be "ROY G. BIV" ("red-orange-yellow-green-blue-indigo-violet"). They are also used as mental checklists, for example in aviation: "GUMPS", which is "gas-undercarriage-mixture-propeller-seatbelts". Other examples of mnemonic acronyms are "CAN SLIM", and "PAVPANIC" as well as "PEMDAS".
Acronyms as legendary etymology
It is not uncommon for acronyms to be cited in a kind of false etymology, called a folk etymology, for a word. Such etymologies persist in popular culture but have no factual basis in historical linguistics, and are examples of language-related urban legends. For example, "cop" is commonly cited as being derived, it is presumed, from "constable on patrol", and "posh" from "port outward, starboard home". With some of these specious expansions, the "belief" that the etymology is acronymic has clearly been tongue-in-cheek among many citers, as with "gentlemen only, ladies forbidden" for "golf", although many other (more credulous) people have uncritically taken it for fact. Taboo words in particular commonly have such false etymologies: "shit" from "ship/store high in transit" or "special high-intensity training" and "fuck" from "for unlawful carnal knowledge", or "fornication under consent/command of the king".
Showing the ellipsis of letters
In English, abbreviations have traditionally been written with a full stop/period/point in place of the deleted part to show the ellipsis of letters – although the colon and apostrophe have also had this role – and with a space after full stops (e.g. "A. D."). In the case of most acronyms, each letter is an abbreviation of a separate word and, in theory, should get its own termination mark. Such punctuation is diminishing with the belief that the presence of all-capital letters is sufficient to indicate that the word is an abbreviation.
Some influential style guides, such as that of the BBC, no longer require punctuation to show ellipsis; some even proscribe it. Larry Trask, American author of The Penguin Guide to Punctuation, states categorically that, in British English, "this tiresome and unnecessary practice is now obsolete."
Pronunciation-dependent style and periods
Nevertheless, some influential style guides, many of them American, still require periods in certain instances. For example, The New York Times Manual of Style and Usage recommends following each segment with a period when the letters are pronounced individually, as in "K.G.B.", but not when pronounced as a word, as in "NATO". The logic of this style is that the pronunciation is reflected graphically by the punctuation scheme.
When a multiple-letter abbreviation is formed from a single word, periods are in general not used, although they may be common in informal usage. "TV", for example, may stand for a single word ("television" or "transvestite", for instance), and is in general spelled without punctuation (except in the plural). Although "PS" stands for the single word "postscript" (or the Latin postscriptum), it is often spelled with periods ("P.S.").
The slash ('/', or solidus) is sometimes used to separate the letters in an acronym, as in "N/A" ("not applicable, not available") and "c/o" ("care of").
Inconveniently long words used frequently in related contexts can be represented according to their letter count as a numeronym. For example, "i18n" abbreviates "internationalization", a computer-science term for adapting software for worldwide use. The "18" represents the 18 letters that come between the first and the last in "internationalization". "Localization" can be abbreviated "l10n", "multilingualization" "m17n", and "accessibility" "a11y". In addition to the use of a specific number replacing that many letters, the more general "x" can be used to replace an unspecified number of letters. Examples include "Crxn" for "crystallization" and the series familiar to physicians for history, diagnosis, and treatment ("hx", "dx", "tx").
Representing plurals and possessives
There is a question about how to pluralize acronyms. Often a writer will add an 's' following an apostrophe, as in "PC's". However, Kate Turabian, writing about style in academic writings, allows for an apostrophe to form plural acronyms "only when an abbreviation contains internal periods or both capital and lowercase letters". Turabian would therefore prefer "DVDs" and "URLs" and "Ph.D.'s". The Modern Language Association and American Psychological Association prohibit apostrophes from being used to pluralize acronyms regardless of periods (so "compact discs" would be "CDs" or "C.D.s"), whereas The New York Times Manual of Style and Usage requires an apostrophe when pluralizing all abbreviations regardless of periods (preferring "PC's, TV's and VCR's").
Possessive plurals that also include apostrophes for mere pluralization and periods appear especially complex: for example, "the C.D.'s' labels" (the labels of the compact discs). In some instances, however, an apostrophe may increase clarity: for example, if the final letter of an abbreviation is "S", as in "SOS's" (although abbreviations ending with S can also take "-es", e.g. "SOSes"), or when pluralizing an abbreviation that has periods.
A particularly rich source of options arises when the plural of an acronym would normally be indicated in a word other than the final word if spelled out in full. A classic example is "Member of Parliament", which in plural is "Members of Parliament". It is possible then to abbreviate this as "M's P". (or similar), as used by former Australian Prime Minister Ben Chifley. This usage is less common than forms with "s" at the end, such as "MPs", and may appear dated or pedantic. In common usage, therefore, "weapons of mass destruction" becomes "WMDs", "prisoners of war" becomes "POWs", and "runs batted in" becomes "RBIs".
The argument that acronyms should have no different plural form (for example, "If D can stand for disc, it can also stand for discs") is in general disregarded because of the practicality in distinguishing singulars and plurals. This is not the case, however, when the abbreviation is understood to describe a plural noun already: For example, "U.S." is short for "United States", but not "United State". In this case, the options for making a possessive form of an abbreviation that is already in its plural form without a final "s" may seem awkward: for example, "U.S.", "U.S.'s", etc. In such instances, possessive abbreviations are often forgone in favor of simple attributive usage (for example, "the U.S. economy") or expanding the abbreviation to its full form and then making the possessive (for example, "the United States' economy"). On the other hand, in speech, the pronunciation "United States's" is sometimes used.
Abbreviations that come from single, rather than multiple, words – such as "TV" ("television") – are usually pluralized without apostrophes ("two TVs"); most writers feel that the apostrophe should be reserved for the possessive ("the TV's antenna").
In some languages, the convention of doubling the letters in the acronym is used to indicate plural words: for example, the Spanish EE.UU., for Estados Unidos ('United States'). This old convention is still followed for a limited number of English abbreviations, such as SS. for "Saints", pp. for the Latin plural of "pages", paginae, or MSS for "manuscripts". In the case of pp. it derives from the original Latin phrase "per procurationem" meaning 'through the agency of'; an English translation alternative is particular pages in a book or document: see pp. 8–88.
The most common capitalization scheme seen with acronyms is all-uppercase (all caps), except for those few that have linguistically taken on an identity as regular words, with the acronymous etymology of the words fading into the background of common knowledge, such as has occurred with the words "scuba", "laser", and "radar": these are known as anacronyms. Anacronyms (note well -acro-) should not be homophonously confused with anachronyms (note well -chron-), which are a type of misnomer.
Small caps are sometimes used to make the run of capital letters seem less jarring to the reader. For example, the style of some American publications, including the Atlantic Monthly and USA Today, is to use small caps for acronyms longer than three letters; thus "U.S." and "FDR" in normal caps, but "nato" in small caps. The acronyms "AD" and "BC" are often smallcapped as well, as in: "From 4004 bc to ad 525".
Words derived from an acronym by affixing are typically expressed in mixed case, so the root acronym is clear. For example, "pre-WWII politics", "post-NATO world", "DNAase". In some cases a derived acronym may also be expressed in mixed case. For example, "messenger RNA" and "transfer RNA" become "mRNA" and "tRNA".
Pronunciation-dependent style and case
Some publications choose to capitalize only the first letter of acronyms, reserving all-caps styling for initialisms, writing the pronounced acronyms "Nato" and "Aids" in mixed case, but the initialisms "USA" and "FBI" in all caps. For example, this is the style used in The Guardian, and BBC News typically edits to this style (though its official style guide, dating from 2003, still recommends all-caps). The logic of this style is that the pronunciation is reflected graphically by the capitalization scheme. However, it conflicts with conventional English usage of first-letter upper-casing as a marker of proper names in many cases; e.g. AIDS stands for acquired immuno-deficiency syndrome which is not a proper name, while Aids is in the style of one.
Some style manuals also base the letters' case on their number. The New York Times, for example, keeps "NATO" in all capitals (while several guides in the British press may render it "Nato"), but uses lower case in "Unicef" (from "United Nations International Children's Emergency Fund") because it is more than four letters, and to style it in caps might look ungainly (flirting with the appearance of "shouting capitals").
Numerals and constituent words
While abbreviations typically exclude the initials of short function words (such as "and", "or", "of", or "to"), this is not always the case. Sometimes function words are included to make a pronounceable acronym, such as CORE (Congress of Racial Equality). Sometimes the letters representing these words are written in lower case, such as in the cases of "TfL" ("Transport for London") and LotR (Lord of the Rings); this usually occurs when the acronym represents a multi-word proper noun.
Numbers (both cardinal and ordinal) in names are often represented by digits rather than initial letters, as in "4GL" ("fourth generation language") or "G77" ("Group of 77"). Large numbers may use metric prefixes, as with "Y2K" for "Year 2000" (sometimes written "Y2k", because the SI symbol for 1000 is "k", not "K", which stands for "kelvin", the SI unit for temperature). Exceptions using initials for numbers include "TLA" ("three-letter acronym/abbreviation") and "GoF" ("Gang of Four"). Abbreviations using numbers for other purposes include repetitions, such as "A2DP" ("Advanced Audio Distribution Profile"), "W3C" ("World Wide Web Consortium"), and T3 (Trends, Tips & Tools for Everyday Living); pronunciation, such as "B2B" ("business to business"); and numeronyms, such as "i18n" ("internationalization"; "18" represents the 18 letters between the initial "i" and the final "n").
Casing of expansions
Authors of expository writing will sometimes capitalize or otherwise distinctively format the initials of the expansion for pedagogical emphasis (for example, writing: "the onset of Congestive Heart Failure (CHF)" or "the onset of congestive heart failure (CHF)"), but this conflicts with the convention of English orthography, which reserves capitals in the middle of sentences for proper nouns; and would be rendered as "the onset of congestive heart failure (CHF)" when following the AMA Manual of Style.
Changes to (or wordplay on) the expanded meaning
Some apparent acronyms or other abbreviations do not stand for anything and cannot be expanded to some meaning. Such pseudo-acronyms may be pronunciation-based, such as "BBQ" (bee-bee-cue), for "barbecue", or "K9" (kay-nine) for "canine". Pseudo-acronyms also frequently develop as "orphan initialisms"; an existing acronym is redefined as a non-acronymous name, severing its link to its previous meaning. For example, the letters of the "SAT", a US college entrance test originally dubbed "Scholastic Aptitude Test", no longer officially stand for anything. The US-based pro-choice organization "NARAL" is another example of this; in that case, the organization changed their name three times, with the long-form of the name always corresponding to the letters "NARAL", before eventually opting to simply be known by the short-form, without being connected to a long-form.
This is common with companies that want to retain brand recognition while moving away from an outdated image: American Telephone and Telegraph became AT&T, "Kentucky Fried Chicken" became "KFC" to de-emphasize the role of frying in the preparation of its signature dishes,[a] and British Petroleum became BP. Russia Today has rebranded itself as RT. American Movie Classics has simply rebranded itself as AMC. Genzyme Transgenics Corporation became GTC Biotherapeutics, Inc.; The Learning Channel became TLC; and American District Telegraph became simply known as ADT.
Pseudo-acronyms may have advantages in international markets:[according to whom?] for example, some national affiliates of International Business Machines are legally incorporated with "IBM" in their names (for example, IBM Canada) to avoid translating the full name into local languages. Likewise, UBS is the name of the merged Union Bank of Switzerland and Swiss Bank Corporation, and HSBC has replaced the long name Hongkong and Shanghai Banking Corporation. Some companies which have a name giving a clear indication of their place of origin will choose to use acronyms when expanding to foreign markets: for example, Toronto-Dominion Bank continues to operate under the full name in Canada, but its U.S. subsidiary is known as TD Bank, just as Royal Bank of Canada used its full name in Canada (a constitutional monarchy), but its now-defunct U.S. subsidiary was called RBC Bank. The India-based JSW Group of companies is another example of the original name (Jindal South West Group) being re-branded into a pseudo-acronym while expanding into other geographical areas in and outside of India.
Redundant acronyms and RAS syndrome
Rebranding can lead to redundant acronym syndrome, as when Trustee Savings Bank became TSB Bank, or when Railway Express Agency became REA Express. A few high-tech companies have taken the redundant acronym to the extreme: for example, ISM Information Systems Management Corp. and SHL Systemhouse Ltd. Examples in entertainment include the television shows CSI: Crime Scene Investigation and Navy: NCIS ("Navy" was dropped in the second season), where the redundancy was likely designed to educate new viewers as to what the initials stood for. The same reasoning was in evidence when the Royal Bank of Canada's Canadian operations rebranded to RBC Royal Bank, or when Bank of Montreal rebranded their retail banking subsidiary BMO Bank of Montreal.
Another common example is "RAM memory", which is redundant because "RAM" ("random-access memory") includes the initial of the word "memory". "PIN" stands for "personal identification number", obviating the second word in "PIN number"; in this case its retention may be motivated to avoid ambiguity with the homophonous word "pin". Other examples include "ATM machine", "EAB bank", "HIV virus", Microsoft's NT Technology, and the formerly redundant "SAT test", now simply "SAT Reasoning Test"). TNN (The Nashville/National Network) also renamed itself "The New TNN" for a brief interlude.