n. A freshwater weed of the frog's-bit family (Hydrocharidaceae), native to America; the waterweed or water thyme.
the GNU version of the Collaborative International Dictionary of English
n. A fresh-water weed of the frog's-bit family (Hydrocharidaceæ), native to America. Transferred to England it became an obstruction to navigation. Called also waterweed and water thyme.
Word Usage
"It is not on anything else in the tank (which includes a plastic plant, gravel, and a couple bunches of anacharis), only the bamboo branches."