decisive vs determinative

decisive is not a noun while determinative is a noun.

Word	Noun	Adjective	Verb	Adverb
decisive	No	Yes	No	No
determinative	Yes	Yes	No	No

decisive (noun)	determinative (noun)
	a determining or causal element or factor
	one of a limited class of noun modifiers that determine the referents of noun phrases

decisive (adjective)	determinative (adjective)
determining or having the power to determine an outcome	having the power or quality of deciding
characterized by decision and firmness
forming or having the nature of a turning point or crisis
unmistakable