Mawson, C.O.S., ed. (1870–1938). Roget’s International Thesaurus. 1922.

Class I. Words Expressing Abstract Relations
Section IV. Order
5. Order as Regards Categories

80. Rule.

   NOUN:REGULARITY, uniformity, constancy, clockwork precision; punctuality (exactness) [See Truth]; even tenor, rut; system; routine (custom) [See Habit]; formula; canon, convention, maxim, rule &c. (form, regulation) [See Precept]; keynote, standard, model; precedent (prototype) [See Prototype]; conformity [See Conformity].
  LAW, capitular or capitulary, gnomology [rare], rèlement [F.], order of things; normality, normalcy; normal state, normal condition, natural state, natural condition, ordinary state, ordinary condition, model state, model condition; standing dish, standing order; Procrustean law; law of the Medes and Persians; hard and fast rule; nature, principle.
   ADJECTIVE:REGULAR, uniform, symmetrical, constant, steady; according to rule (conformable) [See Conformity]; normal, habitual, customary [See Habit]; methodical, orderly, systematic, systematical.
   QUOTATION:Order is heav’n’s first law.—Pope