Was he just a monk before? (5)
I believe the answer is:
prior
'before?' is the definition.
('prior' can be a synonym of 'before')
I cannot understand how the rest of the clue works.
(Other definitions for prior that I've seen before include "Existing earlier" , "Abbott's deputy being earlier?" , "Foregoing - cleric" , "head of a house of friars" , "head of a religious community" .)