The Collaborative International Dictionary of English v.0.48:

Banana \Ba*na"na\ (b[.a]*n[aum]"n[.a]; 277), n. [Sp. banana,
   name of the fruit.] (Bot.)
   A perennial herbaceous plant of almost treelike size (Musa
   sapientum); also, its edible fruit. See Musa.
   [1913 Webster]

   Note: The banana has a soft, herbaceous stalk, with leaves of
         great length and breadth. The flowers grow in bunches,
         covered with a sheath of a green or purple color; the
         fruit is five or six inches long, and over an inch in
         diameter; the pulp is soft, and of a luscious taste,
         and is eaten either raw or cooked. This plant is a
         native of tropical countries, and furnishes an
         important article of food.
         [1913 Webster]

   Banana bird (Zool.), a small American bird (Icterus
      leucopteryx), which feeds on the banana.

   Banana quit (Zool.), a small bird of tropical America, of
      the genus Certhiola, allied to the creepers.
      [1913 Webster]

WordNet (r) 3.0 (2006):

banana
    n 1: any of several tropical and subtropical treelike herbs of
         the genus Musa having a terminal crown of large entire
         leaves and usually bearing hanging clusters of elongated
         fruits [syn: banana, banana tree]
    2: elongated crescent-shaped yellow fruit with soft sweet flesh

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "banana":
   burlesquer, caricaturist, clown, comedian, comic, cutup,
   epigrammatist, funnyman, gag writer, gagman, gagster, humorist,
   ironist, jester, joker, jokesmith, jokester, lampooner, madcap,
   parodist, prankster, punner, punster, quipster, reparteeist,
   satirist, wag, wagwit, wisecracker, wit, witling, zany