declivity vs steep

declivity and steep both are nouns.

Word	Noun	Adjective	Verb	Adverb
declivity	Yes	No	No	No
steep	Yes	Yes	Yes	No

As nouns, steep is a hyponym of declivity; that is, steep is a word with a more specific, narrower meaning than declivity:

Other hyponyms of declivity include downhill.

declivity (noun)	steep (noun)
a downward slope or bend	a steep place (as on a hill)

declivity (adjective)	steep (adjective)
	having a sharp inclination
	of a slope; set at a high angle
	greatly exceeding bounds of reason or moderation

declivity (verb)	steep (verb)
	let sit in a liquid to extract a flavor or to cleanse
	devote (oneself) fully to