Noun air sac has 3 senses
  1. 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
  2. air sac - any of the thin-walled extensions of the tracheae of insects
    --2 is a kind of
    sac
    --2 is a part of insect
  3. air sac - any of the membranous air-filled extensions of the lungs of birds
    --3 is a kind of
    sac
    --3 is a part of bird
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