"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). In general, "astronaut" is the more formal and widely recognized term, while "spaceman" is more informal and can be used in a broader sense.
William Francis Lee III (born December 28, 1946), nicknamed "Spaceman", is an American former professional baseball left-handed pitcher who played in Major League Baseball (MLB) for the Boston Red Sox (1969 1978) and Montreal Expos (1979 1982).