What does freethinking mean?

: a person who thinks freely or independently : one who forms opinions on the basis of reason independently of authority especially : one who rejects or is skeptical of religious dogma.

Is free thinker one word or two?

Freethought (sometimes spelled free thought) is an epistemological viewpoint which holds that beliefs should not be formed on the basis of authority, tradition, revelation, or dogma, and that beliefs should instead be reached by other methods such as logic, reason, and empirical observation.