Nouns

(n)feeder, tributary, confluent, affluenta branch that flows into the main stream

Adjectives

(s)tributary(of a stream) flowing into a larger stream
(s)tributarypaying tribute“a tributary colony”
(s)conducive, contributing, contributive, contributory, tributarytending to bring about; being partly responsible for“working conditions are not conducive to productivity”, “the seaport was a contributing factor in the growth of the city”, “a contributory factor”