English bishop with task to perform (6)
I believe the answer is:
errand
'task to perform' is the definition.
(an errand is a task or job)
'english bishop with' is the wordplay.
'english' becomes 'e' (abbreviation).
'bishop' becomes 'rr' (abbreviation for Right Reverend).
'with' becomes 'and'.
'e'+'rr'+'and'='ERRAND'
(Other definitions for errand that I've seen before include "Short journey to get or bring" , "Short trip with a mission" , "Journey made on someone else's behalf" , "Chore" , "Delivery/collection trip" .)