Dove's call (3)
I believe the answer is:
coo
'dove's call' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for coo that I've seen before include "Soft murmuring sound of a pigeon" , "Sound like a dove" , "Sound made by dove" , "Cry of doves - cry of surprise?" , "Softly say" .)