This dictionary covers the four main types of abbreviation – shortenings, contractions, initialisms, and acronyms.
These four types are as follows:
Shortenings of words usually consist of the first few letters of the full form and are usually spelt with a final full stop when they are still regarded as abbreviations, for example cont. = continued, etc. = et cetera. They may also consist of the stressed syllable of the shortened word, e.g. bus or gym. In cases where they form words in their own right, the full stop is omitted, for example hippo = hippopotamus. Such shortenings are often but not always informal. Some become the standard forms, and the full forms are then regarded as formal or technical, for example bus = omnibus, pub = public house, zoo = zoological garden.
Contractions are abbreviated forms in which letters from the middle of the full form have been omitted, for example Dr = doctor, St = saint or street. Practice varies with regard to adding a full stop, but in modern British usage it is increasingly usual to omit it. Another kind of contraction is the type with an apostrophe marking the omission of letters: can’t = cannot, didn’t = did not, you’ve = you have.
Initialisms are made up of the initial letters of words and are pronounced as separate letters: CIA (or C.I.A.), pm (or p.m.), US (or U.S.). Practice again varies with regard to full stops, with current usage increasingly in favour of omitting them, especially when the initialism consists entirely of capital letters.
Acronyms are initialisms that have become words in their own right, or similar words formed from parts of several words. They are pronounced as words rather than as a series of letters, for example Aids, NATO, FIFA, and do not have full stops. Some become so established they are no longer recognized as acronyms, for example radar, laser and scuba. In many cases the acronym becomes the standard term and the full form is only used in explanatory contexts.