Card to traitor returned (5)
I believe the answer is:
tarot
'card' is the definition.
(tarot cards are used to tell fortunes)
'to traitor returned' is the wordplay.
'traitor' becomes 'rat' (rat can mean a traitor).
'returned' is a reversal indicator.
'to'+'rat'='torat'
'torat' backwards is 'TAROT'.
(Other definitions for tarot that I've seen before include "Sort of cards" , "Pack of cards used in fortune-telling" , "Cards used for fortune telling" , "Arcana cards" , "Playing cards" .)