refractivity vs refractive

refractivity is a noun but refractive is not a noun.

Word	Noun	Adjective	Verb	Adverb
refractivity	Yes	No	No	No
refractive	No	Yes	No	No

refractivity (noun)	refractive (noun)
the physical property of a medium as determined by its index of refraction

refractivity (adjective)	refractive (adjective)
	of or relating to or capable of refraction
	capable of changing the direction (of a light or sound wave)