Mere-wíf
Bosworth & Toller Anglo-Saxon Old English Dictionary - mere-wíf
According to the Old English Dictionary:
es;
- mere-wíf
- n. A water-witch, woman living in a lake (Grendel's mother), Beo. Th. 3042; B. 1519. [O. H. Ger. meri-wíb sirena.] mere-wif