A porpoise is a small cetacean of the family Phocoenidae, and is related to dolphins and whales.
The word porpoise comes from the Middle English porpeys/purpeys, from the Anglo-Norman porpeis/purpeis, from the Old French po(u)rpois/pourpais (porpoise), from the Vulgar Latin *porcopiscis (porpoise), from the Latin porcus (pig) and piscis (fish) [source].
Other (archaic / poetic) English words for porpoises, and dolphins, include: sea hogs, sea pigs, seaswine, or mereswine, from the Old English mereswīn (porpoise).
In French a porpoise is a cochon de mer (“sea pig”), or a marsouin [maʁ.swɛ̃], which comes from the Old English mereswīn (porpoise), or from another Germanic language, such as *mariswīn (porpoise, dolphin) in Old Frankish, meerswijn (dolphin, porpoise) in Middle Dutch, or marsvín (dolphin) in Old Norse. These all come from the Proto-Germanic *mariswīną (dolphin, porpoise) from *mari (sea, ocean, lake) and *swīną (swine, pig) [source].
Related words in modern Germanic languages include:
- Mereswyne/Merswine = porpoise or dolphin in Scots
- Meerscheinchen = guinea pig in German
- marsvín = guinea pig in Icelandic and Faroese
- marsvin = guinea pig or porpoise in Danish and Norwegian
- marsvin = guinea pig in Swedish
- meerzwijn = porpoise in Dutch