Noun

• S: (n) alveolus, air sac, air cell (a tiny sac for holding air in the lungs; formed by the terminal dilation of tiny air passageways)
• S: (n) air sac (any of the thin-walled extensions of the tracheae of insects)
• direct hypernym / inherited hypernym / sister term
• part holonym
• S: (n) air sac (any of the membranous air-filled extensions of the lungs of birds)