Drunken parent with gun is abhorrent (9)
I believe the answer is:
repugnant
'abhorrent' is the definition.
('repugnant' can be a synonym of 'abhorrent')
'drunken parent with gun' is the wordplay.
'drunken' indicates anagramming the letters.
'with' is a charade indicator (letters next to each other).
'parent' after 'gun' is 'gunparent'.
'gunparent' with letters rearranged gives 'REPUGNANT'.
'is' is the link.
(Other definitions for repugnant that I've seen before include "Loathsome" , "Extremely distasteful" , "revolting" , "Abhorrent" , "vile" .)