(a) ?As simple adv., with locative sense and indefinite force: on anything at all, anywhere; (b) as rel. adv. introducing locative adj. clauses: upon which, on which; (c) as subordinating conj. introducing nonlocative adv. clause, with ref. to a situation or series of actions: that said, thus, on the basis of the foregoing, hence [could also be construed as rel. adv. with generalized antecedent].