Creed often ethical, but not entirely (5)
I believe the answer is:
tenet
'creed' is the definition.
(tenet is a kind of creed)
'often ethical but not entirely' is the wordplay.
'not entirely' indicates the answer is hidden within the clue.
'TENET' is hidden in the letters of 'often ethical but'.
(Other definitions for tenet that I've seen before include "Rule" , "Belief held as true" , "Matter of belief" , "Doctrine held to be true" , "Canon" .)