The Collaborative International Dictionary of English v.0.48:

Tenet \Ten"et\, n. [L. tenet he holds, fr. tenere to hold. See
   Tenable.]
   Any opinion, principle, dogma, belief, or doctrine, which a
   person holds or maintains as true; as, the tenets of Plato or
   of Cicero.
   [1913 Webster]

         That al animals of the land are in their kind in the
         sea, . . . is a tenet very questionable. --Sir T.
                                                  Browne.
   [1913 Webster]

         The religious tenets of his family he had early
         renounced with contempt.                 --Macaulay.
   [1913 Webster]

   Syn: Dogma; doctrine; opinion; principle; position. See
        Dogma.
        [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "tenet":
   a belief, article of faith, axiom, belief, canon, code,
   commandment, convention, conviction, credo, creed, dictum,
   doctrine, dogma, form, formula, general principle, golden rule,
   guideline, guiding principle, idea, ideology, imperative, law,
   maxim, mitzvah, moral, norm, opinion, ordinance, persuasion,
   position, precept, principium, principle, regulation, rubric, rule,
   settled principle, standard, teaching, view, viewpoint,
   working principle, working rule