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| air sac (plural air sacs) |
noun |
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| Definition: |
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1. anatomy
Same as alveolus (sense 1)
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2. birds air-filled cavity in bird: an air-filled cavity in a bird, formed as an extension of the respiratory system and growing into the bones, that aids respiration and decreases bone mass
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3. insects respiration aid in insect: a thin-walled bulge diverticulum that aids respiration, located in the tubes that transport air through the bodies of some insects
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