English bishop's sin (3)
I believe the answer is:
err
'sin' is the definition.
(to sin is to err morally)
'english bishop's' is the wordplay.
'english' becomes 'e' (abbreviation).
'bishop' becomes 'rr' (abbreviation for Right Reverend).
'e'+'rr'='ERR'
(Other definitions for err that I've seen before include "Drop a clanger" , "Be incorrect" , "Miss the mark" , "Miscalculate" , "Make mistake in Canberra" .)