A smaller river or stream that flows into a larger river.
From Latin *tributarius* “paying tribute,” from *tributum* “tax, tribute.” The river sense developed by comparing small rivers “paying” their water to a larger one.
A tributary is like a tax‑paying citizen in a water kingdom, sending its flow to a more powerful main river. Look at a river map and you’ll see a branching network that resembles a family tree or even blood vessels.
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