System of principles or beliefs (5)
I believe the answer is:
credo
I believe this clue is a double definition.
'system of principles' is the first definition.
(I've seen this in another clue)
'beliefs' is the second definition.
(a credo is a statement of someone's beliefs)
(Other definitions for credo that I've seen before include "music in church" , "Formal statement of beliefs" , "Set of principles" , "mission statement" , "Mass movement" .)