Adjective
Consisting of, or resembling, air; having the properties of an elastic fluid; gaseous; opposed to dense or solid.
Of or pertaining to air, or to elastic fluids or their properties; pertaining to pneumatics; as, pneumatic experiments.
Moved or worked by pressure or flow of air; as, a pneumatic instrument; a pneumatic engine.
Fitted to contain air; Having cavities filled with air; as, pneumatic cells; pneumatic bones.
Source: Webster's dictionary