Jam quietly disposed of, or set aside? (7)

I believe the answer is:

reserve

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'set aside?' is the definition.
('reserve' can be a synonym of 'set aside')

I don't understand the rest of the clue.

(Other definitions for reserve that I've seen before include "left on the bench?" , "Book - substitute player" , "keep for oneself" , "cool" , "Hold back" .)

I've seen this clue in The Times.

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