Crossword Genius

At the English Market there, decide first pair should be returned, being a bit musty (6)

Ross

I believe the answer is:

corked

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'musty' is the definition.
Both the definition and answer are adjectives. Perhaps they are linked in a way I don't understand?

I don't understand the remainder of the clue.

Can you help me to learn more?

(Another definition for corked that I've seen is " (Wine bottle) spoiled; closed up".)

I've seen this clue in The Irish Times.
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