True edict worked in principle (9)
I believe the answer is:
rectitude
'principle' is the definition.
(thesaurus)
'true edict worked' is the wordplay.
'worked' indicates an anagram.
'true'+'edict'='trueedict'
'trueedict' anagrammed gives 'RECTITUDE'.
'in' is the link.
(Other definitions for rectitude that I've seen before include "Correctness" , "Uprightness, integrity" , "Moral integrity" , "Strict propriety" , "Certitude about moral goodness" .)