Smooth gelato melted (6)
I believe the answer is:
legato
'smooth' is the definition.
('legato' can be similar in meaning to 'smooth')
'gelato melted' is the wordplay.
'melted' is an anagram indicator.
'gelato' is an anagram of 'LEGATO'.
(Other definitions for legato that I've seen before include "play on without pause" , "Smoothly-flowing" , "Smoothly (musical)" , "Don't play roughly" , "Smoothly (mus.)" .)