alveolus

Concise Oxford English Dictionary © 2008 Oxford University Press:
alveolus /alˈvɪələs, ˌalvɪˈəʊləs/

▶noun (pl. alveoli /-lʌɪ, -liː/) Anatomy

• 1 any of the many tiny air sacs of the lungs which allow for rapid gaseous exchange.

• 2 the bony socket for the root of a tooth.

• 3 an acinus (sac-like cavity) in a gland.

– derivatives
alveolate /alˈvɪələt/ adjective.

– origin C17: from L., ‘small cavity’, dimin. of alveus.