contributing vs tributary

contributing is not a noun while tributary is a noun.

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

As adjectives, contributing and tributary are synonyms defined as:

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

Other synonyms of contributing include conducive, contributive, contributory.

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

contributing (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