Church decree or law (5)
I believe the answer is:
canon
I believe this clue is a double definition.
'church decree' is the first definition.
(I've seen this before)
'law' is the second definition.
(I've seen this in another clue)
(Other definitions for canon that I've seen before include "Principle; list of recognised works" , "Round, general rule" , "accepted criterion" , "Collection of writing" , "Body of established rules or principles" .)