Alveolus
Alveolus (al*vē"o*lus) , noun
[Latin, a small hollow or cavity, dim. of alveus: compare French alvéole. See Alveary.]
1.
A cell in a honeycomb.
2.
(Zoology) A small cavity in a coral, shell, or fossil
3.
(Anatomy) A small depression, sac, or vesicle, as the socket of a tooth, the air cells of the lungs, the ultimate saccules of glands, etc.