Other ranks row about a decree (6)
I believe the answer is:
ordain
'decree' is the definition.
(ordaining is a kind of decreeing)
'other ranks row about a' is the wordplay.
'other ranks' becomes 'or' (military abbreviation).
'row' becomes 'din' (both can mean a loud disturbance).
'about' indicates putting letters inside.
'din' enclosing 'a' is 'dain'.
'or'+'dain'='ORDAIN'
(Other definitions for ordain that I've seen before include "Inroad (anag.)" , "Make a decree" , "Make someone a clergyman" , "Invest with priestly authority" , "Decree authoritatively" .)