Merriam-Webster Collegiate Dictionary - alveolus

 noun  (plural alveoli)  Etymology: New Latin, from Latin, diminutive of alveus cavity, hollow, from alvus belly, beehive; akin to Lithuanian aulys beehive, Greek aulos tube, flute  Date: circa 1706  1. a small cavity or pit: as  a. a socket in the jaw for a tooth  b. a small air-containing compartment of the lungs in which the bronchioles terminate and from which respiratory gases are exchanged with the pulmonary capillaries  c. an acinus of a compound gland  d. a cell of a honeycomb  2. teethridge