Decree, one in Arab kingdom judge overlooked (6)
I believe the answer is:
ordain
'decree' is the definition.
(ordaining is a kind of decreeing)
'one in arab kingdom judge overlooked' is the wordplay.
'one' becomes 'i' (Roman numeral).
'in' indicates putting letters inside.
'arab kingdom' becomes 'jordan' (I've seen this before).
'judge' becomes 'j'.
'overlooked' is a deletion indicator.
'i' inserted within 'jordan' is 'jordain'.
'jordain' with 'j' taken away is 'ORDAIN'.
(Other definitions for ordain that I've seen before include "Make a decree" , "Make someone a clergyman" , "Destine" , "Appoint ceremonially to the priesthood" , "Invest with priestly authority" .)