[Fr. huitre, from Gk. ostreon.] A genus of bivalve molluscs, much esteemed for food. Oysters are distributed very widely, and principally in the seas of warm and temperate climates. They are found on gravel and sand, in estuaries, and on the sea-coast, sometimes attached to rocks, trees, etc., at depths varying from the surface to seventeen fathoms. (See Clams.)

0zone. [Gk. ozein, to smell.] A gaseous sub-stance obtained from oxygen ; so named from its peculiar odor, which resembles that of weak chlorine.