ˈhēlēəm noun
( -s )
Usage: often attributive
Etymology: New Latin, from Greek hēlios sun + New Latin -ium — more at solar
: a very light colorless inert gaseous element that is the most difficult of all gases to liquefy, that occurs throughout the universe but in economically extractable amounts only in certain natural gases (as in the Texas panhandle and Kansas), and that is used chiefly in inflating airships and balloons, in arc welding and other metallurgical and chemical processes as an inert gaseous shield, and in diluting oxygen for breathing (as by patients with respiratory ailments and by divers) — symbol He ; see alpha particle; element table