Musical speed (5)
I believe the answer is:
tempo
'musical speed' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tempo that I've seen before include "Rate and rhythm in music" , "Pace of a musical piece" , "Metronome output" , "Speed or beat, musically" , "Speed at which piece of music is played" .)