Clergymen expect to keep up opposition (5)
I believe the answer is:
enemy
'opposition' is the definition.
(I know that opposition can be written as enemy)
'clergymen expect to keep up' is the wordplay.
'to keep' says the answer is hidden in the clue.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'ymene' can be found hidden inside 'clergymen expect'.
'ymene' written backwards gives 'ENEMY'.
(Other definitions for enemy that I've seen before include "is against us" , "Opposing force" , "other side (like 16)" , "Division" , "Hostile person, foe" .)