Lively bit of music (7)
I believe the answer is:
allegro
'lively bit of music' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for allegro that I've seen before include "quickly found in bars?" , "Instruction to perform in lively fashion" , "rather quickly" , "In quick time" , "(In music) a brisk and lively tempo" .)