law, rule, regulation, precept, statute, ordinance, canon mean a principle governing action or procedure.

law implies imposition by a sovereign authority and the obligation of obedience on the part of all subject to that authority.

rule applies to more restricted or specific situations.

regulation implies prescription by authority in order to control an organization or system.

precept commonly suggests something advisory and not obligatory communicated typically through teaching.

statute implies a law enacted by a legislative body.

ordinance applies to an order governing some detail of procedure or conduct enforced by a limited authority such as a municipality.

canon suggests in nonreligious use a principle or rule of behavior or procedure commonly accepted as a valid guide.