"Forty Winks" a cert for tipster (3)

I believe the answer is:

nap

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'forty winks' is the definition.
(synonyms)

I can't explain the rest of the clue.

(Other definitions for nap that I've seen before include "Snatch forty winks" , "A fuzzy surface texture" , "Short sleep on soft surface texture?" , "Siesta" , "Pile of material" .)

I've seen this clue in The Times.

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