Speed, in music (5)
I believe the answer is:
tempo
'speed in music' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tempo that I've seen before include "Metronome output" , "Speed of a musical piece" , "Pace of a musical piece" , "Time (music)" , "Pace of a piece of music" .)