Characteristic feature or mole (7)
I believe the answer is:
traitor
'mole' is the definition.
'characteristic feature or' is the wordplay.
'characteristic feature' becomes 'trait'.
'trait'+'or'='TRAITOR'
(Other definitions for traitor that I've seen before include "Renegade" , "Someone guilty of treason" , "Maclean was one" , "One committing treason" , "Betrayer of a country" .)