Real Dictionary

plantain
variable noun: A plantain is a type of green banana which can be cooked and eaten as a vegetable.

plantain in American English 1
any of a genus (Plantago) of plants of the plantain family, usually with rosettes of basal leaves and spikes of tiny, greenish flowers, including many troublesome weeds
designating a family (Plantaginaceae, order Plantaginales) of dicotyledonous plants
noun: a tropical plant, Musa paradisiaca, of the banana family, resembling the banana

plantain in American English 2
a hybrid banana plant (Musa × paradisiaca) that is widely cultivated in the Western Hemisphere
noun: any plant of the genus Plantago, esp. P. major, a weed with large, spreading leaves close to the ground and long, slender spikes of small flowers

plantain in British English 1
noun: any of various N temperate plants of the genus Plantago, esp P. major ( great plantain), which has a rosette of broad leaves and a slender spike of small greenish flowers: family Plantaginaceae

plantain in British English 2
noun: a large tropical musaceous plant, Musa paradisiaca