wane vs decline

wane and decline both are nouns.

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

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

Other hypernyms of wane include diminution.

As verbs, wane and decline are synonyms defined as:

Other synonyms of wane include go down.

wane (noun)	decline (noun)
a gradual decline (in size or strength or power or number)	a downward slope or bend
	a gradual decrease; as of stored charge or current
	change toward something smaller or lower
	a condition inferior to an earlier condition; a gradual falling off from a better state; decline

wane (verb)	decline (verb)
become smaller	grow smaller
decrease in phase	grow worse
grow smaller	show unwillingness towards
	inflect for number, gender, case, etc.
	go down
	fall in value
	not accept as true