Smooth Italian ice cream setter sent back (6)
I believe the answer is:
legato
'smooth' is the definition.
(musical term)
I can't explain the rest of the clue.
(Other definitions for legato that I've seen before include "scored smoothly" , "Don't play roughly" , "In music, in a smooth even manner" , "In music, the opposite of staccato" , "(Music) without breaks between notes" .)