The Collaborative International Dictionary of English v.0.48:

fanwort \fanwort\ n.
   a common aquatic plant (Cabomba caroliniana) of eastern
   North America having floating and submerged leaves and white
   yellow-spotted flowers.

   Syn: water-shield, Cabomba caroliniana.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

fanwort
    n 1: common aquatic plant of eastern North America having
         floating and submerged leaves and white yellow-spotted
         flowers [syn: water-shield, fanwort, Cabomba
         caroliniana]