Reduce the size of an enclosure? (4)

I believe the answer is:

fold

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'enclosure?' is the definition.
(I know that fold is a type of pen)

I don't understand the remainder of the clue.

(Other definitions for fold that I've seen before include "Congregation; (firm) go bankrupt" , "Tuck - pen" , "enclosure" , "Church following" , "stop functioning" .)

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

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