lighter-than-air

[ lahy-ter-thuh n-air ]
/ ˈlaɪ tər ðənˈɛər /

adjective Aeronautics.

(of an aircraft) weighing less than the air it displaces, hence obtaining lift from aerostatic buoyancy.
of or relating to lighter-than-air craft.

Origin of lighter-than-air

First recorded in 1900–05

British Dictionary definitions for lighter than air

lighter than air

adjective (lighter-than-air when prenominal)

having a lower density than that of air
of or relating to an aircraft, such as a balloon or airship, that depends on buoyancy for support in the air