As interrog. pron. in direct questions referring to a thing or an abstraction: what?, what in the world?

As rel. pron. introducing restrictive adj. clauses: as direct obj., referring to things: which, that; also, referring to persons: whom [difficult to distinguish from sense 3.(b)].

As an independent relative with indefinite or generalizing force referring to a thing, an abstraction, etc., introducing noun clauses: (a) functioning as direct obj. in main clause, with rel. pron. as direct obj. in its own clause: whatever, anything or everything that; (b) functioning as subj. in main clause, with rel. pron. as subj. in its own clause: whatever; also, with clause functioning as appositive to a pron. used as subj. in main clause, with rel. pron. as direct obj. in its own clause, with conditional or concessive force: whatever, if…anything, no matter what [2nd quot.].

As an independent relative with indefinite or generalizing force introducing adv. and adj. clauses, usu. with concessive force: (a) referring to a thing, an abstraction, etc.: no matter what, regardless of what; whatever; (b) referring to a person: no matter what sort of person, no matter who.