The Collaborative International Dictionary
Pimpernel \Pim"per*nel\, n. [F. pimprenelle; cf. Sp. pimpinela, It. pimpinella; perh. from LL. bipinnella, for bipinnula two-winged, equiv. to L. bipennis; bis twice + penna feather, wing. Cf. Pen a feather.] (Bot.) A plant of the genus Anagallis, of which one species ( Anagallis arvensis) has small flowers, usually scarlet, but sometimes purple, blue, or white, which speedily close at the approach of bad weather.
Water pimpernel. (Bot.) See Brookweed.
Water pimpernel \Wa"ter pim"per*nel\ (Bot.) A small white-flowered shrub; brookweed.
WordNet
n. a white-flowered aquatic plant of the genus Samolus
Usage examples of "water pimpernel".
Less important British members of the group are the Chaffweed (Centunculus minimus), one of the smallest among British plants, the Chickweed Wintergreen (Trientalis), the Sea Milk-wort (Glaux maritima), which has succulent salty leaves and has been used as a pickle, and the Common Brookweed or Water Pimpernel (Samolus).