Contribution to co-written ethical opinion (5)
I believe the answer is:
tenet
'opinion' is the definition.
(I've seen this in another clue)
'contribution to co-written ethical' is the wordplay.
'contribution to' indicates a hidden word.
'TENET' is hidden within 'co written ethical'.
(Other definitions for tenet that I've seen before include "Doctrine, dogma, belief" , "Teaching" , "Palindromic principle or belief" , "A palindromic doctrine or belief" , "A belief or credo - it's a palindrome" .)