System of belief constructed on credit (8)
I believe the answer is:
doctrine
'system of belief' is the definition.
'doctrine' can be an answer for 'belief' (doctrine is a kind of belief). I am not certain of the 'system of' bit.
'constructed on credit' is the wordplay.
'constructed' indicates an anagram.
'on'+'credit'='oncredit'
'oncredit' anagrammed gives 'DOCTRINE'.
Can you help me to learn more?
(Other definitions for doctrine that I've seen before include "In credo" , "On credit (anag.)" , "Guiding principle" , "System of beliefs" , "Church's policy" .)