- alveolus, air sac, air cell - a tiny sac for holding air in the lungs; formed by the terminal dilation of tiny air passageways
--1 is a kind of sac
--1 is a part of lung - tooth socket, alveolus - a bony socket in the alveolar ridge that holds a tooth
--2 is a kind of socket
--2 is a part of alveolar ridge, gum ridge, alveolar process