The Collaborative International Dictionary of English v.0.48:

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.]
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   1. An opinion held in opposition to the established or
      commonly received doctrine, and tending to promote a
      division or party, as in politics, literature, philosophy,
      etc.; -- usually, but not necessarily, said in reproach.
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            New opinions
            Divers and dangerous, which are heresies,
            And, not reformed, may prove pernicious. --Shak.
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            After the study of philosophy began in Greece, and
            the philosophers, disagreeing amongst themselves,
            had started many questions . . . because every man
            took what opinion he pleased, each several opinion
            was called a heresy; which signified no more than a
            private opinion, without reference to truth or
            falsehood.                            --Hobbes.
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   2. (Theol.) Religious opinion opposed to the authorized
      doctrinal standards of any particular church, especially
      when tending to promote schism or separation; lack of
      orthodox or sound belief; rejection of, or erroneous
      belief in regard to, some fundamental religious doctrine
      or truth; heterodoxy.
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            Doubts 'mongst divines, and difference of texts,
            From whence arise diversity of sects,
            And hateful heresies by God abhor'd.  --Spenser.
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            Deluded people! that do not consider that the
            greatest heresy in the world is a wicked life.
                                                  --Tillotson.
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   3. (Law) An offense against Christianity, consisting in a
      denial of some essential doctrine, which denial is
      publicly avowed, and obstinately maintained.
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            A second offense is that of heresy, which consists
            not in a total denial of Christianity, but of some
            its essential doctrines, publicly and obstinately
            avowed.                               --Blackstone.
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   Note: "When I call dueling, and similar aberrations of honor,
         a moral heresy, I refer to the force of the Greek ?, as
         signifying a principle or opinion taken up by the will
         for the will's sake, as a proof or pledge to itself of
         its own power of self-determination, independent of all
         other motives." --Coleridge.
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