noun, plural (especially collectively) por·poise, (especially referring to two or more kinds or species) por·pois·es.
verb (used without object), por·poised, por·pois·ing.
Origin of porpoise
noun plural -poises or -poise
Word Origin for porpoise
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.