any of a genus (Cicuta) of perennial plants of the umbel family, with compound umbels of small white flowers and intensely poisonous, tuberous roots, found in the Northern Hemisphere in moist places
See water hemlock in American Heritage Dictionary 4
noun
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.