What may make one warm? (4,3)
I believe the answer is:
thaw out
'warm?' is the definition.
'what may make one' is the wordplay.
'may make' indicates anagramming the letters (I've seen this in other clues).
'one' becomes 'out' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'what' anagrammed gives 'thaw'.
'thaw'+'out'='THAW OUT'
(Other definitions for thaw out that I've seen before include "Defrost" , "Become unfrozen" .)