The DICT Development Group

  buckbean \buckbean\, Buck bean \Buck" bean`\(b[=e]n`). (Bot.)
     A perennial plant ({Menyanthes trifoliata) of Europe and
     America which grows in moist and boggy places, having racemes
     of white, reddish, or purplish flowers and intensely bitter
     trifoliate leaves, sometimes used in medicine; marsh trefoil;
     -- called also bog bean. It often roots at the water margin
     and spreads across the surface.
  
     Syn: water shamrock, bogbean, bog myrtle, marsh trefoil,
          Menyanthes trifoliata.
          [1913 Webster + WordNet 1.5]

  buckbean
      n 1: perennial plant of Europe and America having racemes of
           white or purplish flowers and intensely bitter trifoliate
           leaves; often rooting at water margin and spreading across
           the surface [syn: water shamrock, buckbean, bogbean,
           bog myrtle, marsh trefoil, Menyanthes trifoliata]