an order of marine mammals that comprises the whales, dolphins, and porpoises. These have a streamlined hairless body, no hindlimbs, a horizontal tail fin, and a blowhole on top of the head for breathing.See also Mysticeti, Odontoceti.
modern Latin (plural), from Latin cetus, from Greek kētos 'whale'
Cetacea in other Oxford dictionaries
Definition of Cetacea in the US English dictionary