I. plunge 1 /plʌndʒ/ BrE AmE verb
[ Date: 1300-1400 ; Language: Old French ; Origin: plongier , from Vulgar Latin plumbicare , from Latin plumbum 'lead' ]
1 . [I, T always + adv/prep] to move, fall, or be thrown suddenly forwards or downwards
plunge off/into etc
Her car swerved and plunged off the cliff.
Both the climbers had plunged to their deaths.
2 . [intransitive] if a price, rate etc plunges, it suddenly decreases by a large amount:
The unemployment rate plunged sharply.
plunge to
Oil prices have plunged to a new low.
In the recession, the company’s profits plunged 60%.
3 . [intransitive] literary if a ship plunges, it moves violently up and down because of big waves
plunge in ( also plunge into something ) phrasal verb
1 . to start talking or doing something quickly and confidently, especially without thinking about it first:
It’s a difficult situation. You can’t just plunge in and put everything right.
‘I don’t agree,’ she said, plunging into the conversation.
2 . to jump or ↑ dive into water:
He stripped off and plunged into the sea.
3 . plunge something ↔ in ( also plunge something into something ) to push something firmly and deeply into something else:
He opened the bag and plunged his hand in.
Plunge the pasta into boiling water.
Repeatedly she plunged the knife into his chest.
plunge (somebody/something) into something phrasal verb
to suddenly experience a difficult or unpleasant situation, or to make someone or something do this:
A strike would plunge the country into chaos.
The house was suddenly plunged into darkness.
After the war, the family plunged into debt.
II. plunge 2 BrE AmE noun
1 . take the plunge to decide to do something important or risky, especially after thinking about it for a long time:
We took the plunge and set up our own business.
2 . [countable] a sudden large decrease in the price, value etc of something
plunge in
a dramatic plunge in house prices
3 . [countable usually singular] a sudden movement down or forwards:
The plane began a headlong plunge towards the Earth.
4 . [countable usually singular] when someone suddenly becomes involved in something new
plunge into
his sudden plunge into marriage
5 . [countable usually singular] a jump or ↑ dive into water, or a quick swim
plunge in/into
a quick plunge in the lake