cetacean , a . ( Of the lat. ) Cetus, and this of the g ?t??). 1. adj. Zool. It is said of mammalian pisciformes, marine, some large, who have the nasal openings at the top of the head, which comes out the helmet air whose aqueous vapour, when the atmosphere is cold, tends to condense in the form of nubecillas that simulate water jets. Have previous members transformed into fins, without the later, and the body finished in a single horizontal fin; e.g., the whale and dolphin. They live in all seas. U t. c. s. m. 2. m. pl. Zool. Order of these animals. Or RTOGR. ESCR. with may. initial.