What's about to melt? (4)
I believe the answer is:
thaw
'to melt?' is the definition.
('thaw' can be a synonym of 'melt')
'what's about' is the wordplay.
'about' indicates anagramming the letters.
'what' is an anagram of 'THAW'.
(Other definitions for thaw that I've seen before include "the end of a white Christmas?" , "De-ice" , "when the temperature rises?" , "snow does eventually" , "Become friendlier; melt" .)