Alveolus

n.	1.	A cell in a honeycomb.
	2.	(Zool.) A small cavity in a coral, shell, or fossil
	3.	(Anat.) A small depression, sac, or vesicle, as the socket of a tooth, the air cells of the lungs, the ultimate saccules of glands, etc.

Noun	1.	alveolus - a tiny sac for holding air in the lungs; formed by the terminal dilation of tiny air passageways Synonyms: air cell, air sac
	2.	alveolus - a bony socket in the alveolar ridge that holds a tooth Synonyms: tooth socket

air cell, air sac, lung, sac