air cell
/ˈɛː sɛl/noun
1 Zoology and Anatomy. A specialized air-filled cavity within the body.
2 Botany. An intercellular space in the tissue (especially the stem) of a plant; an air cavity.
3An air-filled compartment or cavity in a manufactured article or natural substance.
Origin
Late 18th century; earliest use found in Philosophical Transactions of the Royal Society of London. From air + cell. In sense 1a perhaps after French cellule aérienne.