Smooth, musically (6)
I believe the answer is:
legato
'smooth musically' 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 "Musically smooth" , "Don't play roughly" , "Smoothly (mus.)" , "Smoothly, musically speaking" , "running into each other" .)