1plunge 
/ˈplʌnʤ/ verb
plung·es; plunged; plung·ing /ˈplʌnʤ/ verb [no obj] 1 always followed by an adverb or preposition : to fall or jump suddenly from a high place
▪ Her car plunged off a bridge. ▪ He plunged [=dove] into the pool. ▪ The rocket plunged [=plummeted] toward the Earth. ▪ The parachute failed to open, and the jumper plunged to her death. [=died from her fall] 2 : to fall or drop suddenly in amount, value, etc. : plummet
▪ The stock market plunged yesterday. ▪ The President's approval rating has plunged to 20 percent. ▪ The moose population has plunged in recent years. 3 always followed by an adverb or preposition : to have a steep slope or drop downward
▪ The rocky cliffs plunge into the swirling rapids below. ▪ The road plunges down the mountain.
▪ Her car plunged off a bridge. ▪ He plunged [=dove] into the pool. ▪ The rocket plunged [=plummeted] toward the Earth. ▪ The parachute failed to open, and the jumper plunged to her death. [=died from her fall]
▪ The stock market plunged yesterday. ▪ The President's approval rating has plunged to 20 percent. ▪ The moose population has plunged in recent years.
▪ The rocky cliffs plunge into the swirling rapids below. ▪ The road plunges down the mountain.
plunge in/into [phrasal verb] 1 plunge (something) in or plunge (something) into (something) : to push (something) into (something) quickly and forcefully
▪ The nurse grabbed his arm and plunged the needle in. ▪ He plunged the knife into the cake. ▪ I plunged the sponge into the bucket of water. ▪ He plunged his hands into his pockets. 2 plunge in or plunge into (something) : to start doing (something) with enthusiasm and energy
▪ It was a big project, so we all just had to plunge in [=dive in] and get started. ▪ She plunged (right) into the assignment. 3 a plunge into (something) : to suddenly begin to be in (a particular and usually bad condition or situation)
▪ He plunged into a severe depression.
b plunge (someone or something) into (something) : to cause (someone or something) to suddenly be in (a particular condition or situation)
▪ A series of bad management decisions had plunged the company into debt. ▪ The author plunges his readers into a world of fantasy. ▪ The museum was recently plunged into scandal when it was learned that some of its art had been sold on the black market. ▪ The city was plunged into darkness. [=the city suddenly became dark]
▪ The nurse grabbed his arm and plunged the needle in. ▪ He plunged the knife into the cake. ▪ I plunged the sponge into the bucket of water. ▪ He plunged his hands into his pockets.
▪ It was a big project, so we all just had to plunge in [=dive in] and get started. ▪ She plunged (right) into the assignment.
▪ He plunged into a severe depression.
b plunge (someone or something) into (something) : to cause (someone or something) to suddenly be in (a particular condition or situation)
▪ A series of bad management decisions had plunged the company into debt. ▪ The author plunges his readers into a world of fantasy. ▪ The museum was recently plunged into scandal when it was learned that some of its art had been sold on the black market. ▪ The city was plunged into darkness. [=the city suddenly became dark]
