Belief in number of commandments from a world beyond (5)
I believe the answer is:
tenet
'belief' is the definition.
(synonyms)
'number of commandments from a world beyond' is the wordplay.
'number of commandments' becomes 'ten' (the Ten Commandments).
'from a world beyond' becomes 'ET' (extra-terrestrial).
'ten'+'et'='TENET'
'in' is the link.
(Other definitions for tenet that I've seen before include "Doctrine held to be true" , "A belief or credo - it's a palindrome" , "A palindromic doctrine or belief" , "Doctrine, dogma, belief" , "A palindromic doctrine or creed" .)