Not  adv. Expressing negation, esp.: 1 (also n't joined to a preceding verb) following an auxiliary verb or be or (in a question) the subject of such a verb (i cannot say; she isn't there; am i not right?). 2 used elliptically for a negative phrase etc. (is she coming? — i hope not; do you want it? — certainly not!).  not at all (in polite reply to thanks) there is no need for thanks. Not half see *half. Not quite 1 almost. 2 noticeably not (not quite proper). [contraction of *nought]