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

(colloquial, sometimes rhetorical question) What is wrong with. / (colloquial, sometimes rhetorical question) What is the reason for.

plural of whatness

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

Asks the interlocutor to identify an indicated object.

(colloquial) What did you just say? / Used other than figuratively or idiomatically: see what, was, that.