tributary (adj.) Look up tributary at Dictionary.com
late 14c., "paying tribute," from Latin tributarius "liable to tax or tribute," from tributum (see tribute).
tributary (n.) Look up tributary at Dictionary.com
late 14c., "person, country, etc. owing obedience or paying tribute or a tax to a sovereign or another people," from Latin tributarius (see tributary (adj.)). Meaning "stream that flows into a larger body" is from 1822, from the adjective in this sense, which is recorded from 1610s.