al·ve·o·lus / alˈvēələs/ • n. (pl. -li / -ˌlī/ ) chiefly Anat. a small cavity, pit, or hollow, in particular: ∎  any of the many tiny air sacs in the lungs where the exchange of oxygen and carbon dioxide takes place. ∎  the bony socket for the root of a tooth. ∎  an acinus in a gland.DERIVATIVES: al·ve·o·late / -lit; -ˌlāt/ adj.

alveolus (al-vee-oh-lŭs) n. (pl. alveoli)
1. (in the lung) a blind-ended air sac of microscopic size.

2. the part of the upper or lower jawbone that supports the roots of the teeth (see also mandible, maxilla).

3. the sac of a racemose gland (see also acinus).

4. any other small cavity, depression, or sac.
—alveolar adj.

alveolus
1. The tiny air sac in the lung of mammals and reptiles at the end of each bronchiole. It is lined by a delicate moist membrane, has many blood capillaries, and is the site of exchange of respiratory gases (carbon dioxide and oxygen).

2. The socket in the jawbone in which a tooth is rooted by means of the periodontal membrane.

alveolus (pl. alveoli) One of a cluster of microscopic tiny air-sacs that open out from the alveolar ducts at the far end of each bronchiole in the lungs. The alveolus is the site for the exchange of gases between the air and the bloodstream, and is covered in a network of capillary blood vessels. See also gas exchange; respiratory system

alveolus small cavity, tooth-socket, etc. XVIII. — L., dim. of alveus trough.
Hence alveolar XVIII. alway †all the time, every time. OE. alne weġ, acc. of ALL and WAY; orig. denoting extent of space or distance, but at its first appearance already transf. to extent of time. Superseded in ordinary use by always XIII.