nosedive vs diminution

nosedive and diminution both are nouns.

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

As nouns, diminution is a hypernym of nosedive; that is, diminution is a word with a broader meaning than nosedive:

Other hypernyms of nosedive include decline.

nosedive (noun)	diminution (noun)
a steep nose-down descent by an aircraft	the act of decreasing or reducing something
a sudden sharp drop or rapid decline	the statement of a theme in notes of lesser duration (usually half the length of the original)
	change toward something smaller or lower

nosedive (verb)	diminution (verb)
plunge nose first; drop with the nose or front first, of aircraft