Definition of porpoise

• n. - Any small cetacean of the genus Phocaena, especially P. communis, or P. phocaena, of Europe, and the closely allied American species (P. Americana). The color is dusky or blackish above, paler beneath. They are closely allied to the dolphins, but have a shorter snout. Called also harbor porpoise, herring hag, puffing pig, and snuffer.
• n. - A true dolphin (Delphinus); -- often so called by sailors.