1. any of certain aquatic plants belonging to the genus Nymphoides, of the gentian family, esp. N. aquatica, having floating, more or less heart-shaped leaves and a cluster of small, white, five-petaled flowers.
2. a related plant, Nymphoides cordata, of North America, having a cluster of white flowers and round or somewhat oval leaves that are purple beneath.
[ 1855-60, Amer. ]