Cusses terribly about Conservative victory (7)
I believe the answer is:
success
'victory' is the definition.
(thesaurus)
'cusses terribly about conservative' is the wordplay.
'terribly' indicates an anagram.
'about' is an insertion indicator.
'conservative' becomes 'c' (abbreviation commonly used in UK politics).
'cusses' is an anagram of 'sucess'.
'sucess' enclosing 'c' is 'SUCCESS'.
(Other definitions for success that I've seen before include "The accomplishment of an aim" , "Positive result; celebrity" , "Achievement of one's aim" , "Victory - attainment" , "The attainment of fame or wealth" .)