A musical ornament (5)
I believe the answer is:
trill
'a musical ornament' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for trill that I've seen before include "bit of birdsong" , "Fast alternation of notes" , "High-pitched warbling sound" , "Rapid alternation of notes" , "sing" .)