The Collaborative International Dictionary of English v.0.48:

Primrose \Prim"rose`\, n. [OE. primerole, F. primerole, a
   derivative fr. LL. primula, from L. primus first. See
   Prime, a.] (Bot.)
   (a) An early flowering plant of the genus Primula (Primula
       vulgaris) closely allied to the cowslip. There are
       several varieties, as the white-, the red-, the
       yellow-flowered, etc. Formerly called also primerole,
       primerolles.
   (b) Any plant of the genus Primula.
       [1913 Webster]

   Evening primrose, an erect biennial herb (Enothera
      biennis), with yellow vespertine flowers, common in the
      United States. The name is sometimes extended to other
      species of the same genus.

   Primrose peerless, the two-flowered Narcissus (Narcissus
      biflorus). [Obs.]
      [1913 Webster]

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.
      [1913 Webster]

            In the ascending scale
            Of heaven, the stars that usher evening rose.
                                                  --Milton.
      [1913 Webster]

   Note: Sometimes, especially in the Southern parts of the
         United States, the afternoon is called evening.
         --Bartlett.
         [1913 Webster]

   2. The latter portion, as of life; the declining period, as
      of strength or glory.
      [1913 Webster]

   Note: Sometimes used adjectively; as, evening gun. "Evening
         Prayer." --Shak.
         [1913 Webster]

   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.
      [1913 Webster]

WordNet (r) 3.0 (2006):

evening primrose
    n 1: any of several plants of the family Onagraceae