Nonstandard except in some dialects. contraction of am not;are not;is not.
Nonstandard. contraction of have not;has not;do not;does not;did not.
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British Dictionary definitions for ain't
am not, is not, are not, have not, or has not: I ain't seen it
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012