Source : Webster's Revised Unabridged Dictionary (1913)

Hippocampus \Hip`po*cam"pus\, n. [L., the sea horse, Gr. ? a
   hippocampus (in senses 1 and 2); "i`ppos horse + ? to bend.]
   1. (Class. Myth.) A fabulous monster, with the head and fore
      quarters of a horse joined to the tail of a dolphin or
      other fish ({Hippocampus brevirostris}), -- seen in
      Pompeian paintings, attached to the chariot of Neptune.
      --Fairholt.