Other forms: plunged, plunging, plunges
To plunge is to go down fast and steeply. A swimmer plunges off the end of the pool, a road plunges down the side of a hill, a bird plunges at the water and comes up with a fish.
Plunge works on money and weather as well as bodies: share prices plunge, temperatures plunge overnight. You also plunge something INTO something — plunge your hands into cold water, plunge a knife into the cake to see if it comes out clean. As a noun a plunge is the drop itself, and "take the plunge" means finally doing the frightening thing you have been putting off: buying the flat, quitting, proposing. A plunger is the rubber cup on a stick for a blocked drain. Plunge is always sudden — a slow decline over years is a decline, not a plunge.
1verbplungeTo fall or dive suddenly and steeply.
“The car left the road and plunged into the river.”
2verbsharplyTo drop sharply in value, level or amount.
“Share prices plunged after the announcement.”
3verbpushTo push something quickly and deeply into something else.
“He plunged his arm into the water right up to the elbow.”
4nounsuddenA sudden dive, fall or drop.
“The plunge in temperature caught everyone out.”
5verbdrainTo clear a blocked drain or toilet by pushing a rubber cup up and down over it.
“If the sink will not empty, plunge it before you call a plumber.”
Too few real examples of this word to estimate which sense is commonest.
Before plunge meant diving, it meant dropping lead. It runs back through Middle English plungen and Old French plongier to a Latin verb built on plumbum, "lead" — plumbicō, to throw a leaded line, the weighted rope sailors dropped over the side to measure the depth. The same plumbum sits inside plumb and plumber. A plunge has been going straight down ever since.
Old French
plongier
Anglo-Norman
plungier
Middle English
plungen
English, today
plunge
Built from
From Middle English plungen, ploungen, Anglo-Norman plungier, from Old French plongier, (Modern French plonger), from unattested Latin - frequentative plumbicō (“to throw a leaded line”), from plumbum (“lead”). Compare plumb, plounce.
Etymology from Wiktionary, CC BY-SA