Edict or maxim (6)
I believe the answer is:
dictum
This clue is a double definition.
'edict' is the first definition.
(thesaurus)
'maxim' is the second definition.
(I've seen this in another clue)
(Other definitions for dictum that I've seen before include "Fiat" , "Authoritative statement" , "Authoritative declaration" , "Statement - saying" , "Popular maxim" .)