A bit off dishonest (6)
I believe the answer is:
rotten
'dishonest' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for rotten that I've seen before include "Nasty" , "unpleasant" , "Decayed or despicable" , "Informally, very much" , "Lousy" .)