Doctrine of equable return (5)
I believe the answer is:
tenet
'doctrine' is the definition.
(both can mean a belief or value)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for tenet that I've seen before include "A palindromic doctrine or creed" , "A belief or credo - it's a palindrome" , "A religious doctrine proclaimed as true without proof" , "A belief or creed - a palindrome" , "Article of belief" .)