water hyacinth

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of several tropical aquatic plants of the genus Eichhornia, especially the widespread species E. crassipes, originally of South America, which forms dense floating masses in rivers and lakes and has large bluish-purple flowers and leafstalks with greatly inflated bases.

from The Century Dictionary.

• noun See Piaiopus.

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

• (Bot.) Either of several tropical aquatic plants of the genus Eichhornia, related to the pickerel weed.

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

• noun a tropical floating aquatic plant having spikes of large blue flowers; troublesome in clogging waterways especially in southern United States