Dictate, prescribe, ordain, decree, impose mean to lay down expressly something to be followed, observed, obeyed, or accepted.
Dictate implies an authoritative direction by or as if by the spoken word which serves in governing or guiding one’s course of action.
Prescribe (see also PRESCRIBE) implies a formulated rule, law, or order; it- suggests an authoritative pronouncement which is clear, definite, and cannot be gainsaid.
Ordain implies institution, establishment, or enactment by a supreme or unquestioned authority or power; usually it suggests an inalterable settlement of a problem or question.
Decree implies a decision made and formally pronounced by absolute authority or by a power whose edicts are received with the same attention.
It is used particularly of ecclesiastical, civil, or judicial power, whether absolute or limited in its scope, or more broadly of anything whose authoritative pronouncements are blindly obeyed.
Impose implies a subjecting to what must be borne, endured, or submitted to. It may suggest infliction by a paramount authority.
More often it suggests limitations intended to make for order, beauty, or efficiency.