Feline sound (4)
I believe the answer is:
purr
'feline sound' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for purr that I've seen before include "Cat's contented sound" , "Soft noise of engine" , "Tiddles' sound" , "Sound of a happy mog" , "Make contented sound like cat" .)