v., n., adv., & adj.
v. 1 intr. & tr. (often foll. by down) drop or fall abruptly (plumped down on the chair; plumped it on the floor). 2 intr. (foll. by for) decide definitely in favour of (one of two or more possibilities). 3 tr. (often foll. by out) utter abruptly; blurt out.
n. an abrupt plunge; a heavy fall.
adv. colloq. 1 with a sudden or heavy fall. 2 directly, bluntly (I told him plump).
adj. colloq. direct, unqualified (answered with a plump 'no').
[ ME f. MLG plumpen, MDu. plompen: orig. imit. ]