Infidel /(?)/

In·fi·del

Infidel

a.
  1. Not holding the faith; -- applied by Christians to one who does not believe in the inspiration of the Scriptures, and the supernatural origin of Christianity; used by Muslims to refer to those who do not believe in Islam.
    The infidel writer is a great enemy to society.
    — V. Knox.

Infidel

n.
  1. One who does not believe in the prevailing religious faith; a heathen; a freethinker; -- used especially by Christians and Muslims.