Comic stand-in so harsh! (9)
I believe the answer is:
dissonant
'harsh' is the definition.
(thesaurus)
'comic stand-in so' is the wordplay.
'comic' indicates anagramming the letters.
'stand'+'in'+'so'='standinso'
'standinso' with letters rearranged gives 'DISSONANT'.
(Other definitions for dissonant that I've seen before include "incongruous" , "grating" , "Lacking harmony" , "sounding harsh" .)