- any of several small, gregarious cetacean mammals of the genus Phocoena, usually blackish above and paler beneath, and having a blunt, rounded snout, especially the common porpoise, P. phocoena, of both the North Atlantic Ocean and the Pacific Ocean.
- any of several small cetacean mammals, as the common dolphin, Delphinus delphis.
- (of a speeding motorboat) to leap clear of the water after striking a wave.
- (of a torpedo) to appear above the surface of the water.
- to move forward with a rising and falling motion in the manner of a porpoise: The car has a tendency to porpoise when overloaded.
- any of various small cetacean mammals of the genus Phocaena and related genera, having a blunt snout and many teeth: family Delphinidae (or Phocaenidae)
- any of various related cetaceans, esp the dolphin
