In folklore, a mermaid is an aquatic creature with the head and upper body of a female human and the tail of a fish.
Mermin
Another English word "†mermin" ( in the OED) for 'siren or mermaid' is older, though now obsolete. It derives from Old English , ad. 'sea' + 'female slave', and the one in Rabenschlacht is a great-grandmother<!-- hence not so much '-maid', as '-woman', Ger. weib or frau, Sw. fru--> of Wittich;