40 winks (6)
(Other definitions for catnap that I've seen before include "For a rest" , "(Tom's) snooze?" , "Drop off" , "Kip" , "Forty winks (for moggy?)" .)
'40 winks' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for nap that I've seen before include "Sleep lightly" , "one akin to whist" , "One likely to win" , "A brief sleep, forty winks" , "A short sleep or snooze" .)