plunge vs power-dive

plunge is a noun but power-dive is not a noun.

Word	Noun	Adjective	Verb	Adverb
plunge	Yes	No	Yes	No
power-dive	No	No	Yes	No

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

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

plunge (noun)	power-dive (noun)
a brief swim in water
a steep and rapid fall

plunge (verb)	power-dive (verb)
begin with vigor	make a power dive
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