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

(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.

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

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

(informal) Alternative form of freedom is not free

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.

Synonym of buy cheap, buy twice

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).

There are more developments yet to come; one should not presume to know the outcome of an event which is still in progress.

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