freethinker

n. One who speculates or forms opinions independently of the authority of others; esp., in the sphere or religion, one who forms opinions independently of the authority of revelation or of the church; an unbeliever; -- a term assumed by deists and skeptics in the eighteenth century. [ 1913 Webster ]

Atheist is an old-fashioned word: I'm a freethinker, child. Addison.

Syn. -- Infidel; skeptic; unbeliever. See Infidel. [ 1913 Webster ]