Mermaid

mermaid
    n 1: half woman and half fish; lives in the sea
    

Mermaid \Mer"maid\, n. [AS. 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.
   [1913 Webster]

   Note: Chaucer uses this word as equivalent to the siren of
         the ancients.
         [1913 Webster]

   {Mermaid fish} (Zool.) the angel fish ({Squatina}).

   {Mermaid's glove} (Zool.), a British branched sponge somewhat
      resembling a glove.

   {Mermaid's head} (Zool.), a European spatangoid sea urchin
      ({Echinocardium cordatum}) having some resemblance to a
      skull.

   {Mermaid weed} (Bot.), an aquatic herb with dentate or
      pectinate leaves ({Proserpinaca palustris} and
      {Proserpinaca pectinacea}).
      [1913 Webster]
    

39 Moby Thesaurus words for "mermaid":
      Davy, Davy Jones, Dylan, Neptune, Nereid, Nereus, Oceanid, Oceanus,
      Poseidon, Thetis, Triton, Varuna, bather, bathing beauty,
      bathing girl, diver, fresh-water nymph, frogman, kelpie, limniad,
      man fish, merman, naiad, natator, nix, nixie, ocean nymph,
      sea devil, sea god, sea nymph, sea-maid, sea-maiden, seaman, siren,
      swimmer, undine, water god, water spirit, water sprite