Use spoon in prison (4)

I believe the answer is:

stir

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'prison' is the definition.
(informal term for prison)

I don't understand how the rest of the clue works.

(Other definitions for stir that I've seen before include "Affect emotionally" , "bird" , "jail" , "Whisk, blend" , "Sensation" .)

I've seen this clue in The Sun.

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