Merriam-Webster's Collegiate® Dictionary, 11th Edition
PLUNGE
I. verb (plunged; plunging)
Etymology: Middle English, from Anglo-French plunger, from Vulgar Latin *plumbicare, from Latin plumbum lead
Date: 14th century
transitive verb to cause to penetrate or enter quickly and forcibly into something , to cause to enter a state or course of action usually suddenly, unexpectedly, or violently , intransitive verb to thrust or cast oneself into or as if into water,
2. to become pitched or thrown headlong or violently forward and downward, to act with reckless haste ; enter suddenly or unexpectedly , to bet or gamble heavily and recklessly, to descend or dip suddenly ,
II. noun
Date: 15th century
an act or instance of plunging ; dive