The Collaborative International Dictionary of English v.0.48:

Asclepias \As*cle"pi*as\, n. [L., fr. Gr. ?, named from
   Asclepios or Aesculapius.] (Bot.)
   A genus of plants including the milkweed, swallowwort, and
   some other species having medicinal properties.
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   Asclepias butterfly (Zool.), a large, handsome, red and
      black butterfly (Danais Archippus), found in both
      hemispheres. It feeds on plants of the genus Asclepias.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Butterfly \But"ter*fly`\, n.; pl. Butterflies. [Perh. from the
   color of a yellow species. AS. buter-fl[=e]ge,
   buttor-fle['o]ge; cf. G. butterfliege, D. botervlieg. See
   Butter, and Fly.] (Zool.)
   A general name for the numerous species of diurnal
   Lepidoptera.

   Note: [See Illust. under Aphrodite.]
         [1913 Webster]

   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.
      [1913 Webster]