Real Dictionary

plunge
verb: If something or someone plunges in a particular direction, especially into water, they fall, rush, or throw themselves in that direction.

plunge in American English
to thrust, throw, or force suddenly (into a liquid, hole, condition, etc.)
intransitive verb: to cast oneself, or fall as if cast, into water, a hole, etc
noun: act of plunging
transitive verb: to cast or thrust forcibly or suddenly into something, as a liquid, a penetrable substance, a place, etc.; immerse; submerge

plunge in British English
noun: a leap or dive as into water
verb: to thrust or throw (something, oneself, etc)