Source : Webster's Revised Unabridged Dictionary (1913)

Milfoil \Mil"foil\, n. [F. mille-feuille, L. millefolium; mille
   thousand + folium leaf. See {Foil} a leaf.] (Bot.)
   A common composite herb ({Achillea Millefolium}) with white
   flowers and finely dissected leaves; yarrow.

   {Water milfoil} (Bot.), an aquatic herb with dissected leaves
      ({Myriophyllum}).

Source : WordNet®

Myriophyllum
     n : chiefly monoecious and usually aquatic herbs (as the
         milfoils) [syn: {genus Myriophyllum}]