from The American Heritage® Dictionary of the English Language, 4th Edition
- Nonstandard Contraction of am not.
- Nonstandard Used also as a contraction for are not, is not, has not, and have not.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- are not, aren’t; is not, isn’t; am not.
- have not, haven’t; has not, hasn’t.
- do not, don’t; does not, doesn’t; did not, didn’t.
from the GNU version of the Collaborative International Dictionary of English
- A contraction for are not and am not; also used for is not. [Colloq. or illiterate speech]. See an't.
from The Century Dictionary and Cyclopedia
- n. A vulgar contraction of the negative phrases am not and are not: often used for is not, and also, with a variant hain't, for have not and has not.
1. From the earlier form an’t, a contraction of am not, are not, and is not. The shift from IPA: /ænt/ to IPA: /eɪnt/ parallels a similar change in some dialects with can’t. In other dialects the pronunciation shifted to IPA: /ɑːnt/, and the spelling aren’t, when used to mean “am not”, is due to the fact that both words are pronounced IPA: /ɑːnt/ in some non-rhotic dialects. Historically, ain’t was present in many dialects of the English language, but not in the southeastern England dialect that became the standard, where it is only found in the construction aren’t I?. (Wiktionary)