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Webster 1913 Edition

Noun.

One who believes wrongly; one who holds a false religion.

Shak.

Noun.

One who believes wrongly; one who holds a false religion.

misbeliever ‎(plural misbelievers)

Someone who holds an unauthorised belief; a heretic, an unbeliever.
- 1603, John Florio, translating Michel de Montaigne, Essayes, London: Edward Blount, OCLC 946730821, II.12:
  We are placed in the country […] where we feare the menaces wherewith she threatneth all mis-beleevers, or follow her promises.