Source : Webster's Revised Unabridged Dictionary (1913)
Air bladder \Air" blad`der\
1. (Anat.) An air sac, sometimes double or variously lobed,
in the visceral cavity of many fishes. It originates in
the same way as the lungs of air-breathing vertebrates,
and in the adult may retain a tubular connection with the
pharynx or esophagus.
2. A sac or bladder full of air in an animal or plant; also
an air hole in a casting.
Source : WordNet®
air bladder
n : an air-filled sac near the spinal column in many fishes that
helps maintain buoyancy [syn: {swim bladder}]