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alveoli

noun, plural al·ve·o·li [al-vee–uh-lahy] /ælˈvi əˌlaɪ/.

a little cavity, pit, or cell, as a cell of a honeycomb.
an air cell of the lungs, formed by the terminal dilation of tiny air passageways.
one of the terminal secretory units of a racemose gland.
the socket within the jawbone in which the root or roots of a tooth are set.

noun plural -li (-ˌlaɪ)

any small pit, cavity, or saclike dilation, such as a honeycomb cell
any of the sockets in which the roots of the teeth are embedded
any of the tiny air sacs in the lungs at the end of the bronchioles, through which oxygen is taken into the blood

1706, from Latin alveolus “a tray, trough, basin; bed of a small river,” diminutive of alvus “belly, stomach, paunch, bowels; hold of a ship,” from PIE *aulo- “hole, cavity” (cf. Greek aulos “tube, pipe,” Old Church Slavonic uliji, Lithuanian aulys “beehive” (hollow trunk), Armenian yli “pregnant”).

n. pl. al•ve•o•li (-lī′)

A small angular cavity or pit, such as a tooth socket or an air sac.

Plural alveoli (ăl-vē′ə-lī′)

Any of the tiny air-filled sacs arranged in clusters in the lungs, in which the exchange of oxygen and carbon dioxide takes place. Also called air sac