The Collaborative International Dictionary of English v.0.48:

Orthodoxy \Or"tho*dox`y\, n. [Gr. ?: cf. F. orthodoxie. See
   Orthodox.]
   1. Soundness of faith; a belief in the doctrines taught in
      the Scriptures, or in some established standard of faith;
      -- opposed to heterodoxy or to heresy.
      [1913 Webster]

            Basil himself bears full and clear testimony to
            Gregory's orthodoxy.                  --Waterland.
      [1913 Webster]

   2. Consonance to genuine Scriptural doctrines; -- said of
      moral doctrines and beliefs; as, the orthodoxy of a creed.
      [1913 Webster]

   3. By extension, said of any generally accepted doctrine or
      belief; the orthodox practice or belief.
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

orthodoxy
    n 1: the quality of being orthodox (especially in religion)
         [ant: heterodoxy, unorthodoxy]
    2: a belief or orientation agreeing with conventional standards
       [ant: heresy, heterodoxy, unorthodoxy]