Feline noise (4)
I believe the answer is:
purr
'feline noise' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for purr that I've seen before include "Appreciative feline sound" , "Make contented sound like cat" , "Noise of a contented feline" , "Soft noise of engine" , "Cat's coo" .)