Turn to a puddle (4)
I believe the answer is:
'turn to a puddle' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for melt that I've seen before include "Reduce from a solid to a liquid state" , "Become liquid by heating" , "Go all weak" , "Become liquefied" , "Dissolve with heat" .)