Bag fastening (5)

I believe the answer is:

catch

This clue is a double definition.

'bag' is the first definition.
('catch' can be a synonym of 'bag')

'fastening' is the second definition.
(catch is a kind of fastening)

(Other definitions for catch that I've seen before include "Arrest" , "Something trapped" , "a sort of 22" , "problem in small print?" , "Discover" .)

I've seen this clue in The Telegraph.

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