Wash away in zero-degree heat (5)
I believe the answer is:
erode
'wash away' is the definition.
(I've seen this in another clue)
'in zero-degree heat' is the wordplay.
'in' says the answer is hidden in the clue.
'ERODE' can be found hidden inside 'zero degree heat'.
(Other definitions for erode that I've seen before include "fragment" , "Abrade" , "Gradually wear away" , "Gradually destroy" , "Corrode" .)