The Collaborative International Dictionary of English v.0.48:

Bittersweet \Bit"ter*sweet`\, n.
   1. Anything which is bittersweet.
      [1913 Webster]

   2. A kind of apple so called. --Gower.
      [1913 Webster]

   3. (Bot.)
      (a) A climbing shrub, with oval coral-red berries
          (Solanum dulcamara); woody nightshade. The whole
          plant is poisonous, and has a taste at first sweetish
          and then bitter. The branches are the officinal
          dulcamara.
      (b) An American woody climber (Celastrus scandens),
          whose yellow capsules open late in autumn, and
          disclose the red aril which covers the seeds; -- also
          called Roxbury waxwork.
          [1913 Webster]