Etymology From Middle English plungen, ploungen, Anglo-Norman plungier, from Old French plongier, (Modern French plonger), from unattested Late Latin frequentative *plumbicō (“to throw a leaded line”), from plumbum (“lead”). Compare plumb, plounce.
To thrust into liquid, or into any penetrable substance; to immerse.
to plunge the body into water
"Most of them don't wash. Those who do usually plunge their head into some brook or rill, if there happens to be one about."1936, Norman Lindsay, The Flyaway Highway, Sydney: Angus and Robertson, page 53:
2
Figuratively To cast, stab or throw deep and fast into some thing, state, condition or action.
to plunge a dagger into the breast
to plunge a nation into war
2 more examples
the city was plunged into darkness
Jon isn’t lying when he tells her she will always be his queen, right before plunging a knife into her. He genuinely swore obedience, and sees himself as a traitor when he commits the deeds.2019 May 19, Alex McLevy, “The final Game Of Thrones brings a pensive but simple meditation about stories (newbies)”, in The A.V. Club, archived from the original on 22 May 2019:
To dive, leap or rush (into water or some liquid); to submerge oneself.
he plunged into the river
5
Figuratively To fall or rush headlong into some thing, action, state or condition.
to plunge into debt
to plunge into controversy
4 more examples
profits plunge 90%
The day was cool and snappy for August, and the Rise all green with a lavish nature. Now we plunged into a deep shade with the boughs lacing each other overhead, and crossed dainty, rustic bridges over the cold trout-streams, the boards giving back the clatter of our horses' feet:[…].1897 December (indicated as 1898), Winston Churchill, chapter VIII, in The Celebrity: An Episode, New York, N.Y.: The Macmillan Company; London: Macmillan & Co., Ltd., →OCLC:
Do we know how kinky practices began? Do we know who the first kinky people were? Well, no. […] Nevertheless, we shall plunge ahead into the past, using what facts we have to make informed assumptions on how we traveled the slippery slope from there to here.2005, Annabelle du Fouet, “The murky world from whence it all came” (chapter 2), in Weather Balloons Make Rotten Sex Toys, Ellora's Cave, →ISBN, page 32:
Target reported profit plunged 90% in the second quarter, falling far short of expectations, as inflation-weary customers pulled back on spending on nonessential items.2022 August 17, Chris Isidore, “Target profit plunges 90% as inflation-weary shoppers pull back”, in CNN:
6
To pitch or throw oneself headlong or violently forward, as a horse does.
[N]ature affects a looſe kinde of liberty, vvhich it cannot indure to have reſtrained: neither fares it othervviſe vvith it, then vvith ſome vvilde colt; which at the firſt taking up, flings and plunges, and vvill ſtand on no ground; but after it hath been ſomvvhile diſciplin'd at the Poſt, is grovvn tractable, and quietly ſubmits either to the ſaddle, or the collar: […]1648, J[oseph] Hall, chapter LXXXVI, in Select Thoughts: Or, Choice Helps for a Pious Spirit. […], London: […] Nath[aniel] Brooke, […], published 1654, →OCLC, pages 249–250:
7
Slang To bet heavily and recklessly; to risk large sums in gambling.
8
Obsolete To entangle or embarrass (mostly used in past participle).
Plunged and gravelled with three lines of Seneca.1650, Thomas Browne, Pseudodoxia Epidemica: […], 2nd edition, London: […] A[braham] Miller, for Edw[ard] Dod and Nath[aniel] Ekins, […], →OCLC:
Etymology From Middle English plungen, ploungen, Anglo-Norman plungier, from Old French plongier, (Modern French plonger), from unattested Late Latin frequentative *plumbicō (“to throw a leaded line”), from plumbum (“lead”). Compare plumb, plounce.