Smoothly, in music (6)
I believe the answer is:
legato
'smoothly in music' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for legato that I've seen before include "scored smoothly" , "In music, the opposite of staccato" , "Smoothly, musically speaking" , "Smoothly (musical)" , "In music, in a smooth even manner" .)