Fruit in a returnable container (3)

I believe the answer is:

nut

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'fruit' is the definition.
(nut is a kind of fruit)

I cannot understand how the remainder of the clue works.

(Other definitions for nut that I've seen before include "Food put in crackers" , "Fan" , "Enthusiastic person" , "Screwing block" , "Hard fruit or informal lunatic" .)

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

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