auxiliary air bag; ballonnet
Technical term used in airships and similar lighter-than-air craft; refers to an internal air-filled compartment that helps control buoyancy and shape.
The ballonnet of an airship serves to adjust for pressure differences caused by altitude changes.
Compound of 空気 (air) and 房 (chamber, compartment). The exact historical derivation is uncertain; the term is a modern technical coinage.