Assyrian's foe (4)
I believe the answer is:
'assyrian's foe' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mede that I've seen before include "who proverbially laid down the law" , "Old Indo-European" , "Ancient native of Persia" , "Lawmaker" , "One of the old folk" .)