precept

axiom, fundamental, maxim

bylaw, ground rule, rule, reg, regulation

code, constitution, decalogue, directory

act, law, ordinance, statute

behest, charge, command, commandment, decree, dictate, direction, directive, edict, fiat, instruction, order

moral, principle, value

ban, interdiction, prohibition, proscription, restriction

convention, custom, habit, manners, mores, practice (also practise), tradition, way

blueprint, canon, formula, guide, guideline, standard