Crossword Genius

This to eat gives one bellyache (6)

Ross

I believe the answer is:

grouse

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'one bellyache' 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 grouse that I've seen before include "Petty complaint" , "1D [GAMEBIRD] < having grumble" , "Gripe; game bird" , "Game bird - beef" , "Grumble like game-bird" .)

I've seen this clue in The Guardian.
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