In early use: any of several plants used medicinally. In later use (specifically): any of various plants which constitute, or were formerly included in, the genus Alisma (family Alismataceae) of aquatic and marshland plants, widespread across north temperate regions; especially water plantain, A. plantago-aquatica, with broad leaves and loose clusters of small white three-petalled flowers, common in ponds and ditches.
Valid publication of the genus name: Linnaeus Species plantarum (1753) I. 342.
Late 16th century; earliest use found in John Banister (1532/3–?1610), surgeon. From post-classical Latin alisma from Hellenistic Greek ἄλισμα water plantain (Dioscorides), of unknown origin.