porpoise: Meaning and Definition of

por•poise

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.

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.