Meaning of air sac

air' sac"

Pronunciation: [key]
  1. a sac containing air.
  2. alveolus (def. 2).
  3. any of certain cavities in a bird's body connected with the lungs.
  4. a saclike dilation of the wall of a trachea in many insects.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.