A member of the opposition in Byzantium? (4)
I believe the answer is:
anti
'a member of the opposition' is the definition.
(I've seen this in another clue)
'in byzantium?' is the wordplay.
'in' says the answer is hidden in the clue.
'ANTI' is hidden within 'byzantium'.
(Other definitions for anti that I've seen before include "An opponent - opposed to party policy, etc" , "one opposing?" , "Opposed to followers of Hitler" , "'No' voter" , "Adversary" .)