Members of a male religious order (8)
I believe the answer is:
brethren
'members of a male religious order' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for brethren that I've seen before include "Lay members of a male religious order" , "Siblings (archaic)" , "Fellow male members" , "Church members" , "Biblical or other old brothers" .)