Rat has characteristic, alternatively (7)
I believe the answer is:
traitor
'rat' is the definition.
(I've seen this in another clue)
'characteristic alternatively' is the wordplay.
'characteristic' becomes 'trait' (a trait is a quality or characteristic).
'alternatively' becomes 'or'.
'trait'+'or'='TRAITOR'
'has' acts as a link.
(Other definitions for traitor that I've seen before include "Someone guilty of treason" , "Maclean was one" , "One betraying one's country" , "Rat riot (anag.)" , "Renegade" .)