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]