Definify.com
Webster 1913 Edition
Air cell
Air′ cellˊ
.1.
(Bot.)
A cavity in the cellular tissue of plants, containing air only.
2.
(Anat.)
A receptacle of air in various parts of the system; as, a cell or minute cavity in the walls of the air tubes of the lungs; the air sac of birds; a dilatation of the air vessels in insects.