1Any aquatic plant with inconspicuous flowers, especially a pondweed.
- ‘I grimaced, I hated pickled waterweed, and by the face mother pulled when she ate it, I suspect she did too.’
- ‘One had tresses of green waterweed hanging in her eyes.’
- ‘He sat on the rock, undulating like a waterweed, brie in one hand, knife in the other.’
2A submerged aquatic American plant that is grown in aquariums and ornamental ponds.
- ‘Be sure to include submergent plants such as common waterweed and hornwort for their high oxygen output.’