Diocese part (6)
I believe the answer is:
parish
'diocese part' is the definition.
('parish' is part of 'diocese')
This is all the clue.
(Other definitions for parish that I've seen before include "Local church community" , "Ecclesiastical area" , "administrative district" , "District with own church and clergyman" , "Kind of 2 down - has rip (anag)" .)