An offence in a fool or comic (7)
I believe the answer is:
amusing
'comic' is the definition.
(thesaurus)
'an offence in a fool' is the wordplay.
'an' becomes 'a'.
'offence' becomes 'sin' (I've seen this before).
'in' is an insertion indicator.
'a fool' becomes 'mug' ('mug' can be a synonym of 'fool'**).
'sin' going inside 'mug' is 'musing'.
'a'+'musing'='AMUSING'
'or' is the link.
(Other definitions for amusing that I've seen before include "Entertaining, pleasing" , "Killing" , "Entertaining in a mild way" , "Comical" , "Causing a smile" .)