steepness vs gradient

steepness and gradient both are nouns.

Word	Noun	Adjective	Verb	Adverb
steepness	Yes	No	No	No
gradient	Yes	No	No	No

As nouns, gradient is a hypernym of steepness; that is, gradient is a word with a broader meaning than steepness:

steepness: the property possessed by a slope that is very steep
gradient: the property possessed by a line or surface that departs from the horizontal

Other hypernyms of steepness include slope.

steepness (noun)	gradient (noun)
the property possessed by a slope that is very steep	the property possessed by a line or surface that departs from the horizontal
	a graded change in the magnitude of some physical quantity or dimension