The Collaborative International Dictionary of English v.0.48:

Plantain \Plan"tain\, n. [Cf. F. plantain-arbre, plantanier, Sp.
   pl['a]ntano, pl['a]tano; prob. same word as plane tree.]
   1. (Bot.) A treelike perennial herb (Musa paradisiaca) of
      tropical regions, bearing immense leaves and large
      clusters of the fruits called plantains. See Musa.
      [1913 Webster]

   2. The fruit of this plant. It is long and somewhat
      cylindrical, slightly curved, and, when ripe, soft,
      fleshy, and covered with a thick but tender yellowish
      skin. The plantain is a staple article of food in most
      tropical countries, especially when cooked.
      [1913 Webster]

   Plantain cutter, or Plantain eater (Zool.), any one of
      several large African birds of the genus Musophaga, or
      family Musophagid[ae], especially Musophaga violacea.
      See Turaco. They are allied to the cuckoos.

   Plantain squirrel (Zool.), a Java squirrel (Sciurus
      plantani) which feeds upon plantains.

   Plantain tree (Bot.), the treelike herb Musa paradisiaca.
      See def. 1 (above).
      [1913 Webster]

WordNet (r) 3.0 (2006):

plantain tree
    n 1: a banana tree bearing hanging clusters of edible angular
         greenish starchy fruits; tropics and subtropics [syn:
         plantain, plantain tree, Musa paradisiaca]