trib·u·tar·y 
(trĭbyə-tĕr′ē)
(trĭbyə-tĕr′ē)n. pl. trib·u·tar·ies
1. A stream that flows into a larger stream or other body of water.
2. A ruler or nation that pays tribute.
adj.
1. Making additions or yielding supplies; contributory.
2. Paid in tribute.
3. Paying tribute: a tributary colony.
[Middle English tributarie, paying tribute, from Latin tribūtārius, from tribūtum, tribute; see TRIBUTE.]