Quaver (5)
I believe the answer is:
trill
'quaver' is the definition.
(synonyms)
This is all the clue.
(Other definitions for trill that I've seen before include "Quavering or vibratory sound" , "High-pitched warbling sound" , "Warbling sound made by a songbird" , "Shrill warble" , "bit of birdsong" .)