Crossword Genius

River known for its port (5)

Ross

I believe the answer is:

douro

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'river' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for douro that I've seen before include "European runner" , "Iberian river" , "Hollow bubbling sound" .)

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