wane vs diminution

wane and diminution both are nouns.

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

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

Other hypernyms of wane include decline.

wane (noun)	diminution (noun)
a gradual decline (in size or strength or power or number)	the act of decreasing or reducing something
	the statement of a theme in notes of lesser duration (usually half the length of the original)
	change toward something smaller or lower