Plunge  —v. (-ging) 1 (usu. Foll. By in, into) a thrust forcefully or abruptly. B dive. C (cause to) enter a condition or embark on a course impetuously (they plunged into marriage; the room was plunged into darkness). 2 immerse completely. 3 a move suddenly and dramatically downward. B (foll. By down, into, etc.) Move with a rush (plunged down the stairs). 4 colloq. Run up gambling debts. —n. Plunging action or movement; dive.  take the plunge colloq. Take a decisive step. [romanic: related to *plumb]