Crossword Genius

Secure document found in chiropodist's (8)

Ross

I believe the answer is:

nailfile

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'chiropodist's' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'secure document' is the wordplay.
'secure' becomes 'nail' (both can mean to apprehend or capture).
'document' becomes 'file' (a file is a formal document).
'nail'+'file'='NAILFILE'

'found in' is the link.

Can you help me to learn more?

(Other definitions for nailfile that I've seen before include "Manicure item" , "Manicurist's tool" .)

I've seen this clue in The Irish Times.
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