Webster's Revised Unabridged Dictionary · 1913

Mermaid

Mermaid , noun

[Anglo-Saxon mere lake, sea. See Mere lake, and maid.]

A fabled marine creature, typically represented as having the upper part like that of a woman, and the lower like a fish; a sea nymph, sea woman, or woman fish.

Chaucer uses this word as equivalent to the siren of the ancients.

Collocations (4)
Mermaid fish (Zoology) , the angel fish (Squatina).
Mermaid's glove (Zoology) , a British branched sponge somewhat resembling a glove.
Mermaid's head (Zoology) , a European spatangoid sea urchin (Echinocardium cordatum) having some resemblance to a skull.
Mermaid weed (Botany) , an aquatic herb with dentate or pectinate leaves (Proserpinaca palustris and Proserpinaca pectinacea).