"Astronaut" is the term commonly used in the United States to refer to individuals who are trained to travel and work in space. "Spaceman" is a more colloquial term that can refer to astronauts or to anyone who travels in space, including cosmonauts (from Russia) and taikonauts (from China).

noun,plural spacemen [speys-men, -muhn]. an astronaut. a visitor to earth from outer space; extraterrestrial.