Bird's chirp (5)
I believe the answer is:
tweet
'bird's chirp' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tweet that I've seen before include "Note of a small bird" , "Chirp of a small bird" , "Sound of small bird" , "Small bird's chirp" , "Birdsong" .)