as·tro·naut [ástr? nàwt] (plural as·tro·nauts) noun 1. space traveler: somebody trained to travel and perform tasks in space 2. immigrant commuting to Asia: an East or Southeast Asian immigrant whose family is settled in Canada, the United States, Australia, or New Zealand but who frequently travels to Asia to work (informal) [Early 20th century. < astro-, after aeronaut]