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. 2. (Zoöl.) A genus of lophobranch fishes of several species in which the head and neck have some resemblance to those of a horse; -- called also se...