Source : Webster's Revised Unabridged Dictionary (1913)

Water hyacinth \Wa"ter hy"a*cinth\ (Bot.)
   Either of several tropical aquatic plants of the genus
   {Eichhornia}, related to the pickerel weed.

Source : WordNet®

water hyacinth
     n : a tropical floating aquatic plant having spikes of large
         blue flowers; troublesome in clogging waterways
         especially in southern United States [syn: {water orchid},
          {Eichhornia crassipes}, {Eichhornia spesiosa}]