Crossword Genius

One's caught by zip fastener (4)

Ross

I believe the answer is:

nail

'fastener' is the definition.
(nail is a kind of fastener)

'one's caught by zip' is the wordplay.
'one' becomes 'a'.
'caught by' is an insertion indicator.
'zip' becomes 'nil' ('nil' can be a synonym of 'zip'**).
'a' placed inside 'nil' is 'NAIL'.

(Other definitions for nail that I've seen before include "Spike, tack" , "Fix with a metal spike" , "for the carpenter?" , "Fastening device" , "thing for keeping things together" .)

I've seen this clue in The Independent.
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