Class as sin a tenet including murder (11)
I believe the answer is:
assassinate
'murder' is the definition.
(thesaurus)
'class as sin a tenet including' is the wordplay.
'including' says the answer is hidden in the clue.
'ASSASSINATE' is hidden in the letters of 'class as sin a tenet'.
(Other definitions for assassinate that I've seen before include "Put an end to" , "Murder a prominent person" , "Murder (a political or religious leader)" , "Kill for a cause" , "Kill for political reasons" .)