Pronunciation: (pôr'pus),[key] —n., pl.(esp. collectively)-poise,(esp. referring to two or more kinds or species)-pois•es, —v.,-poised, -pois•ing.
—n. 1. any of several small, gregarious cetaceans of the genus Phocoena, usually blackish above and paler beneath, and having a blunt, rounded snout, esp. the common porpoise, P. phocoena, of both the North Atlantic and Pacific.
2. any of several other small cetaceans, as the common dolphin, Delphinus delphis.
—v.i. 1. (of a speeding motorboat) to leap clear of the water after striking a wave.
2. (of a torpedo) to appear above the surface of the water.
3. to move forward with a rising and falling motion in the manner of a porpoise: The car has a tendency to porpoise when overloaded.