Pigeon call (3)
I believe the answer is:
coo
'pigeon call' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for coo that I've seen before include "Murmur amorously" , "(Of pigeon) murmur" , "Speak lovingly -- cry softly" , "Murmur lovingly" , "Softly say" .)