sneezewort

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A Eurasian herb (Achillea ptarmica) of the composite family, having aromatic, linear, finely serrate leaves and clusters of white flower heads grouped in corymbs. Also called sneezeweed.

Century Dictionary and Cyclopedia

1. n. In old usage, the white hellebore, Veratrum album, more often under the form neezewort. Britten and Holland, Eng. Plant Names.
2. n. A (composite herb, Achillea Ptarmica, chiefly of the Old World. The flower-heads are larger and much fewer than those of the yarrow, A. Millefolium; the leaves are simple and sharply serrate, and when dried and pulverized are said to provoke sneezing (whence the name).
3. n. Same as sneezeweed.

Wiktionary

1. n. Achillea ptarmica, a hardy flowering plant, poisonous to cattle, sheep and horses, but with various herbal applications in humans.

GNU Webster's 1913

1. n. (Bot.) A European herbaceous plant (Achillea Ptarmica) allied to the yarrow, having a strong, pungent smell.

WordNet 3.0

1. n. Eurasian herb having loose heads of button-shaped white flowers and long grey-green leaves that cause sneezing when powdered