Form of hostility that never heats up? (4,3)
I believe the answer is:
cold war
'form of hostility that never heats up?' is the definition.
'cold war' can be an answer for 'form of hostility'. I'm not certain of the rest of the definition.
'form of hostility' is the wordplay.
'form of' becomes 'cold' (I can't explain this - if you can you should believe this answer much more).
'hostility' becomes 'war' (war is a kind of hostility).
'cold'+'war'='COLD WAR'
(Other definitions for cold war that I've seen before include "Chilly hostility between nations without actual fighting" , "State of tension after 1945" , "State of hostility (rather than hostilities?)" , "Low card (anag.)" , "major stand-off" .)