Some Nazarene: mysterious adversary (5)
I believe the answer is:
enemy
'adversary' is the definition.
(I've seen this before)
'some nazarene mysterious' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'ENEMY' is hidden within 'nazarene mysterious'.
(Other definitions for enemy that I've seen before include "is against us" , "Division" , "Yemen (anag.)" , "Rival" , "Hostile person, foe" .)