The Collaborative International Dictionary of English v.0.48:

Freethinker \Free"think`er\, 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]

WordNet (r) 3.0 (2006):

freethinker
    n 1: a person who believes that God created the universe and
         then abandoned it [syn: deist, freethinker]

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "freethinker":
   big person, broad-gauge person, ecumenicist, esprit fort,
   free lance, free spirit, free trader, humanist, independent,
   individualist, isolationist, latitudinarian, liberal, liberalist,
   libertarian, libertine, mugwump, neutral, nonpartisan,
   rugged individualist, secular humanist, third force, third world