The Collaborative International Dictionary of English v.0.48:

Venus \Ve"nus\ (v[=e]"n[u^]s), n. [L. Venus, -eris, the goddess
   of love, the planet Venus.]
   1. (Class. Myth.) The goddess of beauty and love, that is,
      beauty or love deified.
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   2. (Anat.) One of the planets, the second in order from the
      sun, its orbit lying between that of Mercury and that of
      the Earth, at a mean distance from the sun of about
      67,000,000 miles. Its diameter is 7,700 miles, and its
      sidereal period 224.7 days. As the morning star, it was
      called by the ancients Lucifer; as the evening star,
      Hesperus.
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   3. (Alchem.) The metal copper; -- probably so designated from
      the ancient use of the metal in making mirrors, a mirror
      being still the astronomical symbol of the planet Venus.
      [Archaic]
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   4. (Zool.) Any one of numerous species of marine bivalve
      shells of the genus Venus or family Veneridae. Many of
      these shells are large, and ornamented with beautiful
      frills; others are smooth, glossy, and handsomely colored.
      Some of the larger species, as the round clam, or quahog,
      are valued for food.
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   Venus's basin (Bot.), the wild teasel; -- so called because
      the connate leaf bases form a kind of receptacle for
      water, which was formerly gathered for use in the toilet.
      Also called Venus's bath.

   Venus's basket (Zool.), an elegant, cornucopia-shaped,
      hexactinellid sponge (Euplectella speciosa) native of
      the East Indies. It consists of glassy, transparent,
      siliceous fibers interwoven and soldered together so as to
      form a firm network, and has long, slender, divergent
      anchoring fibers at the base by means of which it stands
      erect in the soft mud at the bottom of the sea. Called
      also Venus's flower basket, and Venus's purse.

   Venus's comb.
      (a) (Bot.) Same as Lady's comb.
      (b) (Zool.) A species of Murex (Murex tenuispinus). It
          has a long, tubular canal, with a row of long, slender
          spines along both of its borders, and rows of similar
          spines covering the body of the shell. Called also
          Venus's shell.

   Venus's fan (Zool.), a common reticulated, fanshaped
      gorgonia (Gorgonia flabellum) native of Florida and the
      West Indies. When fresh the color is purple or yellow, or
      a mixture of the two.

   Venus's flytrap. (Bot.) See Flytrap, 2.

   Venus's girdle (Zool.), a long, flat, ribbonlike, very
      delicate, transparent and iridescent ctenophore (Cestum
      Veneris) which swims in the open sea. Its form is due to
      the enormous development of two spheromeres. See Illust.
      in Appendix.

   Venus's hair (Bot.), a delicate and graceful fern
      (Adiantum Capillus-Veneris) having a slender, black and
      shining stem and branches.

   Venus's hair stone (Min.), quartz penetrated by acicular
      crystals of rutile.

   Venus's looking-glass (Bot.), an annual plant of the genus
      Specularia allied to the bellflower; -- also called
      lady's looking-glass.

   Venus's navelwort (Bot.), any one of several species of
      Omphalodes, low boraginaceous herbs with small blue or
      white flowers.

   Venus's pride (Bot.), an old name for Quaker ladies. See
      under Quaker.

   Venus's purse. (Zool.) Same as Venus's basket, above.

   Venus's shell. (Zool.)
      (a) Any species of Cypraea; a cowrie.
      (b) Same as Venus's comb, above.
      (c) Same as Venus, 4.

   Venus's slipper.
      (a) (Bot.) Any plant of the genus Cypripedium. See
          Lady's slipper.
      (b) (Zool.) Any heteropod shell of the genus Carinaria.
          See Carinaria.
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The Collaborative International Dictionary of English v.0.48:

Hesperus \Hes"pe*rus\, n. [L. See Hesper.]
   1. Venus when she is the evening star; Hesper.
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   2. Evening. [Poetic]
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            The Sun was sunk, and after him the Star
            Of Hesperus.                          --Milton.
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The Collaborative International Dictionary of English v.0.48:

Evening \E"ven*ing\, n. [AS. [=ae]fnung. See even, n., and cf.
   Eve.]
   1. The latter part and close of the day, and the beginning of
      darkness or night; properly, the decline of the day, or of
      the sun.
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            In the ascending scale
            Of heaven, the stars that usher evening rose.
                                                  --Milton.
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   Note: Sometimes, especially in the Southern parts of the
         United States, the afternoon is called evening.
         --Bartlett.
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   2. The latter portion, as of life; the declining period, as
      of strength or glory.
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   Note: Sometimes used adjectively; as, evening gun. "Evening
         Prayer." --Shak.
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   Evening flower (Bot.), a genus of iridaceous plants
      (Hesperantha) from the Cape of Good Hope, with
      sword-shaped leaves, and sweet-scented flowers which
      expand in the evening.

   Evening grosbeak (Zo["o]l.), an American singing bird
      (Coccothraustes vespertina) having a very large bill.
      Its color is olivaceous, with the crown, wings, and tail
      black, and the under tail coverts yellow. So called
      because it sings in the evening.

   Evening primrose. See under Primrose.

   The evening star, the bright star of early evening in the
      western sky, soon passing below the horizon; specifically,
      the planet Venus; -- called also Vesper and Hesperus.
      During portions of the year, Mars, Jupiter, and Saturn are
      also evening stars. See Morning Star.
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WordNet (r) 3.0 (2006):

Hesperus
    n 1: a planet (usually Venus) seen at sunset in the western sky
         [syn: evening star, Hesperus, Vesper]