Forty feline winks? (6)
I believe the answer is:
catnap
'forty' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'feline winks?' is the wordplay.
'feline' becomes 'cat' (cat is a kind of feline).
'winks?' becomes 'nap' (I can't explain this - if you can you should believe this answer much more).
'cat'+'nap'='CATNAP'
Can you help me to learn more?
(Other definitions for catnap that I've seen before include "little snooze" , "Drop off" , "go out briefly" , "(Tom's) snooze?" , "Forty winks (for moggy?)" .)