Yarrow n. : 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.

Example:
I have a problem with Yarrow spreading throught my yard. How can I get rid of it?

Taxonomy
yarrow, Achillea millefolium, subsp, plant, the leaves, flowers, species, stems, yarrow stalks, nosebleed, herb, Yarrow flowers, yarrow oil, Yarrow tea, yarrow plant, unranked, woundwort, leaf.

Defination from the web:
yarrow is an erect herbaceous perennial plant that produces one to several stems (0.2 to 1m tall) and has a rhizomatous growth form. ... In the Middle Ages, yarrow was part of a herbal mixture known as gruit used in the flavouring of beer prior to the use of hops. ...