alveolus vs air cell

alveolus and air cell both are nouns.

As nouns, alveolus and air cell are synonyms defined as:

alveolus and air cell: a tiny sac for holding air in the lungs; formed by the terminal dilation of tiny air passageways

Other synonyms of alveolus include air sac.

alveolus (noun)	air cell (noun)
a tiny sac for holding air in the lungs; formed by the terminal dilation of tiny air passageways	a tiny sac for holding air in the lungs; formed by the terminal dilation of tiny air passageways
a bony socket in the alveolar ridge that holds a tooth