Principal church of a diocese (9)
I believe the answer is:
cathedral
'principal church of a diocese' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for cathedral that I've seen before include "dramatic murder location" , "Principal 2 down of diocese" , "Carted Hal off to church" , "Where one worships" , "Principal church of see" .)