air-space (n.)

also airspace, by 1821 in reference to stove and furnace construction, from air (n.1) + space (n.). From 1852 in reference to the cubic contents of a room (with reference to the persons in it) in sanitary regulations for boarding rooms, hospitals, etc. In firearms, "a vacant space between the powder charge and the projectile" (1847). By 1910 as "portion of the atmosphere controlled by a country above its territory."