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]

WordNet (r) 3.0 (2006):

tenet
    n 1: a religious doctrine that is proclaimed as true without
         proof [syn: dogma, tenet]

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



Bouvier's Law Dictionary, Revised 6th Ed (1856):

TENET. Which he holds. There are two ways of stating the tenure in an action
of waste. The averment is either in the tenet and the tenuit; it has a
reference to the time of the waste done, and not to the time of bringing the
action.
     2. When the averment is in the tenet the plaintiff on obtaining a
verdict, will recover the place wasted, namely, that part of the premises in
which the waste was exclusively done, if it were done in a par only,
together with treble damages. But when the averment is in the tenuit, the
tenancy being at an end, he will have judgment for his damages only. 2
Greenl. Ev. 652.