Source : Webster's Revised Unabridged Dictionary (1913)

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 : WordNet®

yarrow
     n : ubiquitous strong-scented mat-forming Eurasian herb of
         wasteland, hedgerow or pasture having narrow serrate
         leaves and small usually white florets; widely
         naturalized in North America [syn: {milfoil}, {Achillea
         millefolium}]