But·ter·fly n.; pl. Butterflies   Zool. A general name for the numerous species of diurnal Lepidoptera. 
  Note: [See Illust. under Aphrodite.]
  Asclepias butterfly. See under Asclepias.
  Butterfly fish Zool., the ocellated blenny (Blennius ocellaris) of Europe. See Blenny. The term is also applied to the flying gurnard.
  Butterfly shell Zool., a shell of the genus Voluta.
  Butterfly valve Mech., a kind of double clack valve, consisting of two semicircular clappers or wings hinged to a cross rib in the pump bucket. When open it somewhat resembles a butterfly in shape.
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  butterfly fish
       n : small usually brilliantly colored tropical marine fishes
           having narrow deep bodies with large broad fins; found
           worldwide