Faith, belief system (8)
I believe the answer is:
religion
This clue is a double definition.
'faith' is the first definition.
(I know that faith can be written as religion)
'belief system' is the second definition.
(I know that religion is a type of belief system)
(Other definitions for religion that I've seen before include "System of divine worship" , "Marx's pium of the people" , "Institution for worship" , "Institution to express belief in a divine power" , "Belief in and worship of god or gods" .)