■ verb
1》 fall or move suddenly and uncontrollably.
↘jump or dive quickly and energetically.
↘(often ~ in ) embark impetuously on a speech or course of action.
2》 push or thrust quickly.
↘( ~ someone/thing into ) suddenly bring someone or something into a specified condition or state.
■ noun an act of plunging.
Phrases
take the ~ informal commit oneself to a bold course of action after consideration.
Origin
ME: from OFr. plungier 'thrust down', based on L. plumbum 'lead, plummet'.