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 (A. 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.

Source: Webster's Revised Unabridged Dictionary (1913)