Yarrow \Yar"row\, n. [OE. yarowe, yarwe, [yogh]arowe, AS. gearwe; akin to D. gerw, OHG. garwa, garawa, G. garbe, schafgarbe, and perhaps to E. yare.]

(Bot.) An American and European composite plant (Achillea Millefolium) with very finely dissected leaves and small white corymbed flowers. It has a strong, and somewhat aromatic, odor and taste, and is sometimes used in making beer, or is dried for smoking. Called also milfoil, and nosebleed.

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: Webster's Revised Unabridged Dictionary (1913)