Imitate a dove (3)
I believe the answer is:
coo
'imitate a dove' is the definition.
(a dove's noise is a coo)
This is all the clue.
(Other definitions for coo that I've seen before include "Murmur of a dove" , "Breathe" , "Soft murmuring sound of a pigeon" , "Speak lovingly -- cry softly" , "Make loving sounds -bill and . . ." .)