determinative vs decisive

determinative is a noun but decisive is not a noun.

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

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

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