contributive vs tributary

contributive is not a noun while tributary is a noun.

Word	Noun	Adjective	Verb	Adverb
contributive	No	Yes	No	No
tributary	Yes	Yes	No	No

As adjectives, contributive and tributary are synonyms defined as:

contributive and tributary: tending to bring about; being partly responsible for

Other synonyms of contributive include conducive, contributing, contributory.

contributive (noun)	tributary (noun)
	a branch that flows into the main stream

contributive (adjective)	tributary (adjective)
tending to bring about; being partly responsible for	tending to bring about; being partly responsible for
	paying tribute
	(of a stream) flowing into a larger stream