water parsnip

from The Century Dictionary.

• noun A plant of the genus Sium, especially S. latifolium. See cut under skirret.

from the GNU version of the Collaborative International Dictionary of English.

• (Bot.) Any plant of the aquatic umbelliferous genus Sium, poisonous herbs with pinnate or dissected leaves and small white flowers.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun stout white-flowered perennial found wild in shallow fresh water; northern United States and Asia