drop-off vs waning

drop-off and waning both are nouns.

Word	Noun	Adjective	Verb	Adverb
drop-off	Yes	No	No	No
waning	Yes	Yes	No	No

As nouns, waning is a hyponym of drop-off; that is, waning is a word with a more specific, narrower meaning than drop-off:

Other hyponyms of drop-off include shrinkage, shrinking, casualty, sinking, attrition, rarefaction, dwindling, dwindling away.

drop-off (noun)	waning (noun)
a change downward	a gradual decrease in magnitude or extent
a steep high face of rock
a noticeable deterioration in performance or quality

drop-off (adjective)	waning (adjective)
	(of the Moon) pertaining to the period during which the visible surface of the moon decreases