Chestnuts in the granary (4)

I believe the answer is:

corn

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'chestnuts in the granary' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

This is all the clue.

Can you help me to learn more?

(Other definitions for corn that I've seen before include "falling on deaf ears?" , "Grain; hard skin" , "Hard growth on foot" , "Something unoriginal - cereal plant" , "Crop - growth" .)

I've seen this clue in The Globe and Mail.

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