An official order, especially one that is given in a forceful and unfair way. (Cambridge Dictionary)
A proclamation having the force of law. (Merriam – Webster)
An edict is a command or instruction given by someone in authority. (Collins Dictionary)
An official order or proclamation issued by a person in authority. (Oxford Dictionaries)
A brief summary and significance of the edict of Milan.
The Edict of Milan.