chairman (n.) 1650s, "occupier of a chair of authority," from chair (n.) + man (n.). The meaning "member of a corporate body chosen to preside at meetings" is from c. 1730. Chairwoman in this sense is attested from 1699; chairperson from 1971.

Chairman is a traditional title for the leader of a committee or other such body. The origin is, as one might guess, a compound of the words chair + man. The chair is a reference to a seat or position of authority and the man is, of course, a reference to the person who occupies it.