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

Inside their heads, whales have phonic lips and an air sac that looks similar to how humans manipulate sound. — Molly McCrea, CBS News, 12 Feb. 2026

The delicate air sacs that normally transfer oxygen into the bloodstream had stiffened and scarred. — Bill Frist, Forbes.com, 17 Mar. 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

Males fan their tails, inflate air sacs and produce popping sounds to attract females, according to the National Audubon Society. — Samantha Agate, Miami Herald, 14 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