Reversible principle? (5)
I believe the answer is:
tenet
This clue is a double definition.
'reversible' is the first definition.
'principle?' is the second definition.
(a tenet is a principle or value)
(Other definitions for tenet that I've seen before include "Teaching" , "It's believed" , "A belief or credo - it's a palindrome" , "Item of belief" , "Palindromic principle or belief" .)