plunge vs nosedive

plunge and nosedive both are nouns.

Word	Noun	Adjective	Verb	Adverb
plunge	Yes	No	Yes	No
nosedive	Yes	No	Yes	No

As verbs, nosedive is a hyponym of plunge; that is, nosedive is a word with a more specific, narrower meaning than plunge:

Other hyponyms of plunge include power-dive, duck, crash-dive, chute, jump, parachute.

plunge (noun)	nosedive (noun)
a brief swim in water	a steep nose-down descent by an aircraft
a steep and rapid fall	a sudden sharp drop or rapid decline

plunge (verb)	nosedive (verb)
begin with vigor	plunge nose first; drop with the nose or front first, of aircraft
devote (oneself) fully to
cause to be immersed
immerse briefly into a liquid so as to wet, coat, or saturate
thrust or throw into
fall abruptly
drop steeply
dash violently or with great speed or impetuosity