water hemlock

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of several poisonous, heavy-scented, perennial herbs of the genus Cicuta, especially C. maculata, of marshy areas in eastern and central North America, having compound umbels of small white flowers and bipinnately compound leaves.

Century Dictionary and Cyclopedia

1. n. See Cicuta.
2. n. The hemlock water-dropwort, Œnanthe crocata, otherwise called dead-tongue; also Œ. Phellandrium, distinguished as fine-leafed water-hemlock.

GNU Webster's 1913

1. A poisonous umbelliferous plant (Cicuta virosa) of Europe; also, any one of several plants of that genus.
2. A poisonous plant (Œnanthe crocata) resembling the above.

WordNet 3.0

1. n. tall erect highly poisonous Eurasiatic perennial herb locally abundant in marshy areas