An aeronaut is someone who flies an aircraft: a pilot. Originally, an aeronaut was specifically someone who flew a balloon.
This word looks a lot like astronaut, and it means something similar: a pilot. Though an aeronaut can be someone who pilots any kind of flying vehicle, this word has most commonly applied to people who fly balloons: balloonists. In the mid-1800's, pioneering scientist and inventor Thaddeus S. C. Lowe made a record balloon journey from Cincinnati to South Carolina, thus becoming an early claimant to this word, which had been coined late in the previous century.