A pocket to watch? (3)

I believe the answer is:

fob

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'a pocket' is the definition.
(fob is a kind of pocket)

I cannot understand how the rest of the clue works.

(Other definitions for fob that I've seen before include "Small watch pocket" , "It is worn hanging from a watch-chain" , "Key-ring tab" , "Ornament worn on watch chain" , "Ornament worn on a watch-chain" .)

I've seen this clue in the Evening Standard.

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