plunge

1 plunge /ˈplʌnʤ/ verb
plunges; plunged; plunging
1 plunge
/ˈplʌnʤ/
verb
plunges; plunged; plunging
Britannica Dictionary definition of PLUNGE
[no object]
1 
always followed by an adverb or preposition : to fall or jump suddenly from a high place
2 
: to fall or drop suddenly in amount, value, etc. : plummet
3 
always followed by an adverb or preposition : to have a steep slope or drop downward

plunge in/into

[phrasal verb]
1 
plunge (something) in or plunge (something) into (something) : to push (something) into (something) quickly and forcefully
2 
plunge in or plunge into (something) : to start doing (something) with enthusiasm and energy
3 
a  plunge into (something) : to suddenly begin to be in (a particular and usually bad condition or situation)
b  plunge (someone or something) into (something) : to cause (someone or something) to suddenly be in (a particular condition or situation)
2 plunge /ˈplʌnʤ/ noun
plural plunges
2 plunge
/ˈplʌnʤ/
noun
plural plunges
Britannica Dictionary definition of PLUNGE
[count]
1 
: a sudden fall or jump usually from a high place
2 
: a sudden quick fall in amount, value, etc.
3 
: the act of suddenly beginning to be in a particular condition or situation — usually + into

take the plunge

informal
: to do something after thinking about it especially for a long time