English Noun mountain sickness (uncountable) (medicine) Altitude sickness. 1915 April, Enos A. Mills, “Going to the Top”, in The Rocky Mountain Wonderland, Houghton Mifflin, →LCCN, →OCLC, page 10:Mountain-sickness, with its nausea, first comes to those who are bilious, or to those who are hurrying or exerting themselves more than usual. Translations altitude sickness — see altitude sickness See also Altitude sickness on Wikipedia.Wikipedia Wikiwand - on Seamless Wikipedia browsing. On steroids.