dirigible balloon
Historical term for a steerable lighter-than-air craft; now largely replaced by 飛行船 (airship).
Dirigible balloons were used from the late 19th century to the early 20th century.
Compound of 軽気 (light gas, referring to hydrogen or helium) and 球 (balloon, sphere). The exact historical derivation is uncertain, but the term reflects early aviation terminology.