Parent with gun, awfully offensive (9)
I believe the answer is:
repugnant
'offensive' is the definition.
('repugnant' can be similar in meaning to 'offensive')
'parent with gun awfully' is the wordplay.
'with' is a charade indicator (letters next to each other).
'awfully' indicates an anagram.
'parent' put after 'gun' is 'gunparent'.
'gunparent' anagrammed gives 'REPUGNANT'.
(Other definitions for repugnant that I've seen before include "Very unwelcome" , "Unacceptable" , "revolting" , "Offensive to the mind" , "Abhorrent" .)