Senior cleric’s blunder over work (6)
I believe the answer is:
bishop
'senior cleric's' is the definition.
(a bishop is a senior clergyman)
'blunder over work' is the wordplay.
'blunder' becomes 'bish' (I've seen this before).
'over' says to put letters next to each other (in a down clue, some letters go over others).
'work' becomes 'op' (abbreviation for opus).
'bish'+'op'='BISHOP'
(Other definitions for bishop that I've seen before include "Head of a diocese" , "High-ranking clergyman" , "See man at the top" , "He wears the mitre and carries the crozier" , "He wields the crosier" .)