(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.
any of several small, gregarious cetaceans 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 and Pacific.
any of several other small cetaceans, as the common dolphin, Delphinus delphis.
Jake disengaged the autopilot—it had a tendency to porpoise the plane when the receiving aircraft pushed in the drogue—and devoted his attention to maintaining a smooth, steady course on the great circle.
-- Stephen Coonts, Flight of the Intruder, 1986
We hit another wave and were thrown up again, and this time we began to porpoise.
-- Tom Casey, Strangers' Gate, 2006
Porpoise entered English in the fifteenth century from the Old French porc + peis literally meaning "pork fish." It is thought that this name was given to the marine animal because its snout resembled a pig snout.