The story
- Proto-Germanic · inherited from*mariswīną“dolphin, porpoise, cetacean”
- Proto-West Germanic · inherited from*mariswīn
- Old English · inherited frommereswīn“porpoise, dolphin”
- Middle English · inherited frommereswyn“porpoise, dolphin”
- English todaymereswine
Inherited from Middle English mereswyn (“porpoise, dolphin”), from Old English mereswīn (“porpoise, dolphin”), from Proto-West Germanic *mariswīn, from Proto-Germanic *mariswīną (“dolphin, porpoise, cetacean”). By surface analysis, mere + swine or mer- + swine.
Etymology from Wiktionary, CC BY-SA 4.0.