Crossword Genius

Disappointment of French omitted from their paper (5)

Ross

I believe the answer is:

lemon

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'paper' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for lemon that I've seen before include "Strong yellow colour" , "A fruit; a worthless item" , "Leaving body" , "Sharp-tasting fruit" , "Pulsate" .)

I've seen this clue in The Times.
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