The Collaborative International Dictionary of English v.0.48:

Heterodoxy \Het"er*o*dox`y\, n. [Gr. ?: cf. F.
   h['e]t['e]rodoxie.]
   An opinion or doctrine, or a system of doctrines, contrary to
   some established standard of faith, as the Scriptures, the
   creed or standards of a church, etc.; heresy. --Bp. Bull.
   [1913 Webster]

WordNet (r) 3.0 (2006):

heterodoxy
    n 1: any opinions or doctrines at variance with the official or
         orthodox position [syn: unorthodoxy, heterodoxy,
         heresy] [ant: orthodoxy]
    2: the quality of being unorthodox [syn: unorthodoxy,
       heterodoxy] [ant: orthodoxy]