The Collaborative International Dictionary of English v.0.48:

Freethinking \Free"think`ing\, n.
   Undue boldness of speculation; unbelief. --Berkeley.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

free-thinking \free-thinking\ adj.
   inclined to forms one's own opinions rather than depend upon
   authority, especially about social and religious issues;
   exhibiting boldness of speculation; skeptical of authority.

   Syn: latitudinarian, undogmatic, undogmatical.
        [WordNet 1.5 + 1913 Webster]

WordNet (r) 3.0 (2006):

free-thinking
    adj 1: unwilling to accept authority or dogma (especially in
           religion) [syn: free-thinking, latitudinarian,
           undogmatic, undogmatical]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "freethinking":
   broad-minded, broad-mindedness, catholicity, free thought,
   humanism, latitudinarian, latitudinarianism, liberal, liberalism,
   liberalistic, liberality, liberalness, liberation, libertarian,
   libertarianism, libertine, libertinism, open-minded,
   open-mindedness, secular humanism, tolerance, tolerant, toleration,
   unbigoted, unbigotedness