Source : Webster's Revised Unabridged Dictionary (1913)

Heresy \Her"e*sy\, n.; pl. {Heresies}. [OE. heresie, eresie, OF.
   heresie, iresie, F. h['e]r['e]sie, L. haeresis, Gr. ? a
   taking, a taking for one's self, choosing, a choice, a sect,
   a heresy, fr. ? to take, choose.]

Source : WordNet®

heresy
     n 1: any opinions or doctrines at variance with the official or
          orthodox position [syn: {unorthodoxy}, {heterodoxy}]
          [ant: {orthodoxy}]
     2: a belief that rejects the orthodox tenets of a religion
        [syn: {unorthodoxy}]