a contraction of not: didn't; hadn't; couldn't; shouldn't; won't; mustn't.
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British Dictionary definitions for -n't
not: used as an enclitic after be and have when they function as main verbs and after auxiliary verbs or verbs operating syntactically as auxiliariescan't; don't; shouldn't; needn't; daren't; isn't
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