merwife means A mermaid. Lexicurio rates it Rare gem — a strength score of 83 out of 100.
Why “merwife” is a great word
MERWIFE — [Noun] A mermaid, especially one conceived of as a water-witch or supernatural female being of the sea. From Old English merewīf ("water witch, mermaid"), from Proto-West Germanic *mariwīb, from Proto-Germanic *mariwībą ("mermaid, siren"), a compound of *mari ("sea") and *wībą ("woman, wife"). Unlike mermaid, which suggests a romanticized hybrid, or siren, a classical singer of lethal song, a merwife is an archaic folkloric witch of the water. She is the shadow in the peat-dark tarn, the webbed hand brushing the hull of a foundering skiff, the face glimpsed in storm-foam not as an invitation but as a verdict—the deep's resident intelligence, patient and absolute.
Etymology
From Old English merewīf (“water witch, mermaid”), from Proto-West Germanic *mariwīb, from Proto-Germanic *mariwībą (“mermaid, siren”). By surface analysis, mer- + wife. Cognate with Old High German meriwīb.