Liquefied by heating (6)
I believe the answer is:
melted
'liquefied by heating' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for melted that I've seen before include "Liquefied by heating" , "Liquified" , "Liquefied through heat (6)" , "Like liquefied ice" , "Became liquefied" .)