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