Heated hostility to being married (4)
I believe the answer is:
warm
'heated' is the definition.
(I've seen this before)
'hostility to being married' is the wordplay.
'hostility' becomes 'war' (war is a kind of hostility).
'to being married' becomes 'm' (abbreviation, e.g. in genealogy).
'war'+'m'='WARM'
(Other definitions for warm that I've seen before include "Getting close to target" , "Affectionate - balmy" , "Affectionate; quite hot" , "showing enthusiasm" , "Having moderate heat" .)