Cē-tā'ce-ā, n. pl.

n. pl. [From Lat. cetus, Gr. κῆτος, whale.] (Zoöl.) An order of vertebrated mammiferous marine animals, including the whale kind. There are four groups or families; the Balæna family, having an arrangement of whalebone in the mouth, and no teeth, as the common right whale; the Physeter family, having teeth in the lower jaw, as the spermaceti whale; the Dolphin family, including the smaller species, in which both jaws have teeth, as the dolphins, porpoises, &c.; the Monodon or Narwhal family, having one or two tusks instead of teeth. See WHALE.