Definition: astronaut [ΛΓ¦stΙΛrΙΚn] n. 1. A person who performs space or earthwork missions. 2. a person employed by NASA as an astronaut, space weather physicist, or other related field. 3. an individual, especially a professional in a field involving space exploration or astronomy. 4. a person employed by NASA as an astronaut. The word "astronaut" is derived from the Latin term "astron," which means "out of sight" and "star." The name "astronaut" was first used in 1963 for an American astronaut named Eugene Cernan, who flew into space on Apollo 8. However, the term became more widely known and used in English as a generic term for any professional or private individual employed by NASA to perform space missions. The word is often used in reference to a person who has been selected for astronaut training and chosen to participate in space exploration missions. Astronauts have typically completed rigorous training programs, undergo rigorous physical training, and may spend up to six months on the International Space Station (ISS) before being released back into Earth orbit.