outer space outer space {n.} What is outside of the earth's air. An astronaut cannot live without oxygen when he goes into outer space. Categories: add yours {n.} Source: A Dictionary of American Idioms by A. Makkai, M.T. Boatner, J.E. Gates © 2024 To section: O Subscribe to: American IdiomsIdioms feedEnglish languageHome page and general feed Comment on this entry