air sac

noun

1

: one of the air-filled spaces in the body of a bird connected with the air passages of the lungs

2

: alveolus sense 1b

3

: a thin-walled dilation of a trachea occurring in many insects

Examples of air sac in a Sentence

Recent Examples on the Web

Unlike resilin in other insects, for which the protein typically acts as a passive energy storage system or exoskeleton protection, the resilin in these lake flies plays an active role in ensuring their air sacs don’t implode at depth. — Mary Randolph, Scientific American, 23 July 2026

Matthews and his team were intrigued by how this mechanism works, but realized that using air sacs to regulate buoyancy while diving presents a problem. — Margherita Bassi, Popular Science, 23 July 2026

Nagatitan belonged to a subgroup of sauropods that possessed bones with lots of internal air sacs and thin walls, traits that lightened their skeletons. — Reuters, NBC news, 15 May 2026

And inside the actual pillow, there are only those air sacs, which inflate and deflate to slightly change pressure points throughout the night – silently and without disturbing your slumber, or anyone else's. — New Atlas, 20 Apr. 2026

Word History

First Known Use

circa 1805, in the meaning defined at sense 1

Rhymes for air sac

• aback
• attack
• backpack
• backtrack
• bareback
• blackjack
• brownback
• buyback
• callback
• cognac
• comeback
• cutback

Kids Definition

air sac

noun

1

: one of the air-filled spaces connected with the lungs of a bird

2

: one of the thin-walled microscopic pouches in which gases are exchanged in the lungs

Medical Definition

air sac

noun

: alveolus sense b