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Abbreviations

abbreviate (verb): make shorter; shorten (a word or words)
abbreviation (noun): a short form of a word or words

An abbreviation is a short form of a word or phrase. All of the short forms that you see below ↓ are abbreviations.

Dr - Co. - Ltd - c.o.d - NASA - laser - let's - DVD - radar - a.s.a.p. - etc. - FAQ - HTML

There are four main types of abbreviation, and the way that we write, punctuate and pronounce any abbreviation depends largely on its type:

shortening
continued → cont.

contraction
Doctor → Dr

initialism
British Broadcasting Corporation → BBC

acronym
subscriber identification module → sim

Note that the division of abbreviation categories shown above is for basic guidance. In reality, some categories may have sub-categories and other categories can exist, especially in specialized language such as medical or scientific English or concerning foreign words used in English.

Shortenings

A shortening is an abbreviation where the end of the full word has been cut off, like this:

approx.[imately] approx.

Occasionally the front of the full word may be cut off:

[tele]phone phone

And very occasionally the front and end of the full word are cut off:

[in]flu[enza] flu

Here are some more examples:

shortening full form
cont. continued
Corp. Corporation
enc. enclosed
Nov. November
Prof. Professor
ad advertisement
app application
zoo zoological garden
bike bicycle
wellies wellingtons

Note that some shortenings (the last five here, for example) have entered the language as words or informal words, that is, some people may be unaware that they are abbreviations of something longer. Notice too that for such shortenings there may sometimes be a slight change of spelling (bike, wellies).

Punctuation

How do we punctuate shortenings? Do we put a full stop/period at the end?

For abbreviations that we use like words (the last five above, for example), we do not use a full stop at the end.

For the rest (the first five in the table above, for example), this is to some extent a question of style. Some writers and publishers prefer the modern approach and use no full stop. Others prefer a more traditional approach and use a full stop (which indicates that the rest of the word is missing). You can use either style, but the important thing is to be consistent.

If the full form starts with a capital letter, then the shortening must start with a capital letter (Monday → Mon., approximately → approx.)

Pronunciation

Shortenings that are designed to save space in writing are usually (but not always) spoken like the full form (so we typically say "continued" not "cont.").

write: cont. - Corp. - enc. - Nov. - Prof.

say: continued - Corporation - enclosed - November - Professor

Shortenings that are designed to save time and effort in speaking are of course spoken in the short form.

say and write: ad - app - zoo - bike - wellies

shortening (noun): Shortenings are abbreviations in which the beginning or end of the word has been dropped. In some cases both the beginning and the end have been omitted. - Oxford Dictionaries

Contractions

A contraction is an abbreviation where a bit of the full word has been cut out from inside, like this:

D[octo]r Dr

Sometimes more than one bit has been cut out from inside:

L[imi]t[e]d Ltd

And sometimes bits are cut out from inside more than one word:

you[ ha]'ve you've

Here are some more examples:

contraction full form
dept department
ft foot, feet
govt government
Revd Reverend
St Saint
Blvd Boulevard
mfg manufacturing
can't cannot
let's let us
she'd've she would have

Punctuation

Some people put a full stop at the end (govt., Revd.) but strictly speaking there is no need because the last letter of the contraction is the same as the last letter of the full form (govt, Revd).

In contractions of more than one word, the missing letters are replaced by an apostrophe (can't, she'd've).

Pronunciation

Some contractions are written contractions designed to save space in text. We almost always pronounce these in full—the same as the full form.

write: dept - ft - govt - Revd - St - Blvd - mfg

say: department - foot or feet - government - Reverend - Saint - Boulevard - manufacturing

Other contractions are spoken contractions designed to save time and effort in speaking. The written version is simply mimicking the spoken version.

say and write: can't - let's - she'd've

contraction (noun): Contractions are a type of abbreviation in which letters from the middle of the word are omitted. - Oxford Dictionaries

Initialisms

An initialism is an abbreviation made from the initial (first) letters of a group of words (and pronounced as individual letters), like this:

B[ritish] B[roadcasting] C[orporation] BBC

Sometimes only the more important letters are included:

M[ember] [of] P[arliament] MP

Here are some more examples:

initialism full form
ATM automatic teller machine
BA Bachelor of Arts
CD compact disc
CEO Chief Executice Officer
DIY do it yourself
NSA National Security Agency
PLC Public Limited Company
PTO please turn over
UN United Nations
VAT value added tax
VIP very important person

Punctuation

How do we punctuate initialisms? Do we put a full stop/period after each letter?

This is largely a matter of style. Some people prefer the modern approach and use no full stop. Others take a more tradional approach and use a full stop. So CEO and C.E.O. are both acceptable. The important thing is to be consistent.

If the initial letters of the full form are capital letters, then the initialism should also use capital letters (National Security Agency → NSA). If the full form does not require capitals, then the initialism can usually be with or without capitals—it's a matter of style (please turn over → PTO or pto).

Note that some initialisms can also be acronyms. For example, the abbreviation for Value Added Tax (or value added tax) is:

Pronunciation

We usually pronounce initialisms as individual letters—or else we say the full form.

write and say: ATM - BA - CD - CEO - DIY - NSA - PLC - PTO - UN - VAT - VIP

initialism (noun): An abbreviation consisting of initial letters pronounced separately (e.g. BBC) - Oxford Dictionaries

Acronyms

An acronym is an abbreviation made from the initial (first) letters of a group of words (and pronounced as a word), like this:

N[orth] A[tlantic] T[reaty] O[rganization] NATO

Sometimes only the more important first letters are included:

O[rganization] [of the] P[etroleum] E[xporting] C[ountries] OPEC

And sometimes the first two or three letters of a word may be used:

ra[dar] d[etection] a[nd] r[anging] radar

Here are some more examples:

acronym full form
Aids acquired immune deficiency syndrome
laser light amplification by stimulated emission of radiation
NASA National Aeronautics and Space Administration
PIN personal identification number
quango quasi-autonomous non-governmental organization
scuba self-contained underwater breathing apparatus
sim subscriber identification module
TEFL Teaching English as a Foreign Language
UNESCO United Nations Educational, Scientific and Cultural Organization
vat value added tax

Punctuation

Generally speaking, acronyms are not punctuated at all. There is no need to use full stops/periods.

If the acronym's full form uses capital letters, then the acronym usually uses capitals too (National Aeronautics and Space Administration → NASA). Some acronyms may be written with the first letter uppercase and the rest lowercase (acquired immune deficiency syndrome → Aids). Many acronyms have developed into words in their own right and may use entirely lowercase (subscriber identification module [card] → sim [card]).

Whether to use capitals or not is often a matter of style. If in doubt over the name of an organization (for example NASA or Nasa?) you can usually follow the organization's preferred style found on its website. For more general acronyms, a good dictionary will usually show the standard form.

Note that some acronyms can also be initialisms. For example, the abbreviation for Value Added Tax (or value added tax) is:

Pronunciation

All acronyms can be pronounced as words, and many of them have indeed become dictionary words in their own right.

write and say: Aids - laser - NASA - PIN - quango - scuba - sim - TEFL - UNESCO - vat

acronym (noun): An abbreviation formed from the initial letters of other words and pronounced as a word (e.g. ASCII, NASA) - Oxford Dictionaries