Vibrato (7)
I believe the answer is:
tremolo
'vibrato' is the definition.
(I know that tremolo is a type of vibrato)
This is the entire clue.
(Other definitions for tremolo that I've seen before include "Vibrato effect" , "Wavering note" , "Violin's rapid repetition of a single note" , "Musical wavering effect" , "Shaky effect in music" .)