(dialectal or informal) Am not. / (dialectal or informal) Are not, aren’t; is not, isn’t; am not. / (dialectal or informal) Have not, haven’t; has not, hasn’t, when used as an auxiliary.

(slang) Used to express disapproval of an action. / Used other than figuratively or idiomatically: see that, ain't, it.

(colloquial) That is very true; I agree (often with a gloomy or pessimistic tone).

When it comes to sexual satisfaction, penis size doesn't matter, but technique does. / (more generally) The tools you use to accomplish a goal are not as important as what you do with them.

(African-American Vernacular) (It, he, she) is not important; it doesn't matter.

(informal) Alternative form of freedom is not free

Synonym of buy cheap, buy twice

Alternative form of there's no such thing as a free lunch

Alternative form of it's not the whistle that pulls the train

Leave something alone; avoid attempting to correct, fix, or improve what is already sufficient (often with an implication that the attempted improvement is risky and might backfire).