fish any of various cold-blooded, aquatic vertebrates, having gills, commonly fins, and typically an elongated body covered with scales. (loosely) any of various other aquatic animals. the flesh of fishes used as food. Fishes, Astronomy, Astrology. the constellation or sign of Pisces. Informal. a person: an odd fish; a poor fish. a long strip of wood, iron, etc., used to strengthen a mast, joint, etc. Cards Slang. an incompetent player whose incompetence can be exploited.