(informal) A speculation as to what might have happened if something else had happened earlier.

(informal) To speculate about the consequences of something that could have happened.

(idiomatic) Or something else; allows for the existence of an unexpressed alternative to what was said.

Used to introduce a suggestion or proposal for a future event. / Used to introduce a speculation about a future event.

(idiomatic, dated) Something of the kind, whatever (used to terminate a vague list).

(by ellipsis) Used to express astonishment or incredulity, as a question or questioning of the situation at hand, without requiring any specific vulgarity as intensifier.

(slang, African-American Vernacular) A casual greeting.

Alternative spelling of whatnot

plural of whatness

(philosophy) Essence; quiddity. / Quality; quantity.