Definition of cetacean
: any of an order (Cetacea) of aquatic mostly marine mammals that includes the whales, dolphins, porpoises, and related forms and that have a torpedo-shaped nearly hairless body, paddle-shaped forelimbs but no hind limbs, one or two nares opening externally at the top of the head, and a horizontally flattened tail used for locomotion
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Merriam-Webster unabridged
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Time Traveler for cetacean
The first known use of cetacean was in 1840
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