Meaning of “plunge” - Learner’s Dictionary

plunge

verb uk us /plʌndʒ/
plunge down/into, etc

to fall or move down very quickly and with force:

The car came off the road and plunged down the hillside.
He plunged into the water.

[ I ] to become lower in temperature, value, etc very suddenly and quickly:

Temperatures plunged below zero.

(Definition of “plunge verb” from the Cambridge Learner’s Dictionary © Cambridge University Press)