plunge 
(plŭnj)
(plŭnj)v. plunged, plung·ing, plung·es
v.intr.
1.
a. To dive, jump, or throw oneself: We plunged into the lake.
b. To fall rapidly: The car went off the road and plunged into the gully.
2. To devote oneself to or undertake an activity earnestly or wholeheartedly: I plunged into my studies. She plunged ahead with her plan.
3. To enter or move headlong through something: The hunting dogs plunged into the forest.
4. To slope steeply downward: a cliff that plunges to the sea.
5. To move forward and downward violently: The ship plunged through rough seas.
6. To become suddenly lower; decrease dramatically: Stock prices plunged during the banking crisis.
v.tr.
1. To thrust or throw forcefully into a substance or place: plunged the eggs into the hot water; plunged the fork into the potato.
2. To cast suddenly, violently, or deeply into a given state or situation: "The street was plunged in cool shadow" (Richard Wright).
3. To use a plunger to try to unblock (a drain, for example).
n.
Idiom: 1. The act or an instance of plunging: a plunge off the dock.
2. A swim; a dip.
3. A sudden or dramatic decline: a plunge in prices.
take the plunge Informal
To begin an unfamiliar venture, especially after hesitating: After a three-year engagement, they're finally taking the plunge.
[Middle English plungen, from Old French plongier, from Vulgar Latin *plumbicāre, to heave a sounding lead, from Latin plumbum, lead.]