Source : Webster's Revised Unabridged Dictionary (1913)

Heretic \Her"e*tic\, n. [L. haereticus, Gr. ? able to choose,
   heretical, fr. ? to take, choose: cf. F. h['e]r['e]tique. See
   {Heresy}.]
   1. One who holds to a heresy; one who believes some doctrine
      contrary to the established faith or prevailing religion.

            A man that is an heretic, after the first and second
            admonition, reject.                   --Titus iii.
                                                  10.

   2. (R. C. Ch.) One who having made a profession of Christian
      belief, deliberately and pertinaciously refuses to believe
      one or more of the articles of faith ``determined by the
      authority of the universal church.'' --Addis & Arnold.

   Syn: {Heretic}, {Schismatic}, {Sectarian}.

   Usage: A heretic is one whose errors are doctrinal, and
          usually of a malignant character, tending to subvert
          the true faith. A schismatic is one who creates a
          schism, or division in the church, on points of faith,
          discipline, practice, etc., usually for the sake of
          personal aggrandizement. A sectarian is one who
          originates or is an ardent adherent and advocate of a
          sect, or distinct organization, which separates from
          the main body of believers.

Source : WordNet®

heretic
     n 1: a person who holds religious beliefs in conflict with the
          dogma of the Roman Catholic Church [syn: {misbeliever},
          {religious outcast}]
     2: a person who holds unorthodox opinions in any field (not
        merely religion)