Freethinker :: 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..
Thinker :: Thinker (n.) One who thinks; especially and chiefly, one who thinks in a particular manner; as, a close thinker; a deep thinker; a coherent thinker..
Unthinker :: Unthinker (n.) A person who does not think, or does not think wisely..