Sinful, wicked (9)
I believe the answer is:
nefarious
This clue is a double definition.
'sinful' is the first definition.
(thesaurus)
'wicked' is the second definition.
(similar in meaning)
(Other definitions for nefarious that I've seen before include "Extremely wicked" , "Wicked, criminal" , "immoral?" , "Very bad" , "Villainous" .)