Porpoise

[pawr-puh s] /ˈpɔr pəs/

noun, plural (especially collectively) porpoise (especially referring to two or more kinds or species) porpoises.
1.
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.
2.
any of several other small cetaceans, as the common dolphin, Delphinus delphis.
verb (used without object), porpoised, porpoising.
3.
(of a speeding motorboat) to leap clear of the water after striking a wave.
4.
(of a torpedo) to appear above the surface of the water.
5.
to move forward with a rising and falling motion in the manner of a porpoise:
The car has a tendency to porpoise when overloaded.
/ˈpɔːpəs/
noun (pl) -poises, -poise
1.
any of various small cetacean mammals of the genus Phocaena and related genera, having a blunt snout and many teeth: family Delphinidae (or Phocaenidae)
2.
(not in technical use) any of various related cetaceans, esp the dolphin
n.

early 14c., porpas, from Old French porpais (12c.) “porpoise,” literally “pork fish,” from porc “pork” (see pork (n.)) + peis “fish,” from Latin piscis “fish” (see fish (n.)).

The Old French word probably is a loan-translation of a Germanic word meaning literally “sea-hog, mere-swine;” cf. Old Norse mar-svin, Old High German meri-swin, Middle Dutch mereswijn “porpoise” (the last of which also was borrowed directly into French and became Modern French marsouin).

Classical Latin had a similar name, porculus marinus (in Pliny), and the notion behind the name likely is a fancied resemblance of the snout to that of a pig.