Detest running heat (4)
I believe the answer is:
hate
'detest' is the definition.
(synonyms)
'running heat' is the wordplay.
'running' is an anagram indicator.
'heat' anagrammed gives 'HATE'.
(Other definitions for hate that I've seen before include "Passionately dislike" , "powerful emotion" , "[OPPOSITE OF] Be besotted with" , "Detest" , "Odium" .)