'freethinker' originates from English, specifically a compound of 'free' and 'thinker', where 'free' (from Old English 'frēo') meant 'not bound, independent' and 'think' (from Old English 'þencan') meant 'to consider or reflect'.

'freethinker' arose as a compound in early modern English (notably in the 17th–18th centuries) combining 'free' + agent-noun 'thinker'; the component words trace back to Old English roots and the compound came to be used in contexts of religious and philosophical dissent.

Initially it meant 'a person who forms opinions independently'; over time the term came to be especially associated with those who question or reject religious authority and orthodox doctrines.