v. & n.
--v.
1. (usu. foll. by in, into) a tr. thrust forcefully or abruptly. b intr. dive; propel oneself forcibly. c intr. & tr. enter or cause to enter a certain condition or embark on a certain course abruptly or impetuously (they plunged into a lively discussion; the room was plunged into darkness).
2 tr. immerse completely.
3 intr. a move suddenly and dramatically downward. b (foll. by down, into, etc.) move with a rush (plunged down the stairs). c diminish rapidly (share prices have plunged).
4 intr. (of a horse) start violently forward.
5 intr. (of a ship) pitch.
6 intr. colloq. gamble heavily; run into debt.
--n. a plunging action or movement; a dive.
Phrases and idioms:
plunging (or plunge) neckline a low-cut neckline. take the plunge colloq. commit oneself to a (usu. risky) course of action.
Etymology: ME f. OF plungier ult. f. L plumbum plummet