Cleric’s blunder before work (6)
I believe the answer is:
bishop
'cleric's' is the definition.
(type of cleric)
'blunder before work' is the wordplay.
'blunder' becomes 'bish' (I've seen this before).
'before' is a charade indicator (letters next to each other).
'work' becomes 'op' (abbreviation for opus).
'bish'+'op'='BISHOP'
(Other definitions for bishop that I've seen before include "Senior cleric" , "Church dignitary" , "see supervisor" , "Senior churchman" , "Chess piece and one of the clergy" .)