Vivacity, in music (4)
I believe the answer is:
brio
'vivacity in music' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for brio that I've seen before include "Liveliness, maybe in music" , "In music, con ..... means with dash and verve" , "'Con ..., musically with vigour (4)'" , "Sparkle" , "Enthusiasm" .)