Medium's medium (5)
I believe the answer is:
tarot
'medium's medium' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tarot that I've seen before include "Fortune teller's seventy eight card pack" , "Pack member" , "Pack of cards used in fortune-telling" , "Sort of card" , "Cards often used in fortune-telling" .)