buckthorn

from WordNet (r) 3.0 (2006)

buckthorn
    n 1: a shrub or shrubby tree of the genus Rhamnus; fruits are
         source of yellow dyes or pigments
    2: any shrub or small tree of the genus Bumelia
    3: an Old World plantain with long narrow ribbed leaves widely
       established in temperate regions [syn: {English plantain},
       {narrow-leaved plantain}, {ribgrass}, {ribwort}, {ripple-
       grass}, {buckthorn}, {Plantago lanceolata}]

from The Collaborative International Dictionary of English v.0.48

Buckthorn \Buck"thorn`\, n. (Bot.)
   A genus ({Rhamnus}) of shrubs or trees. The shorter branches
   of some species terminate in long spines or thorns. See
   {Rhamnus}.
   [1913 Webster]

   {Sea buckthorn}, a plant of the genus {Hippopha["e]}.
      [1913 Webster]