The Collaborative International Dictionary of English v.0.48:

Iguana \I*gua"na\, n. [Sp. iguana, from the native name in
   Haiti. Cf. Guana.] (Zool.)
   Any species of the genus Iguana, a genus of large American
   lizards of the family Iguanid[ae]. They are arboreal in
   their habits, usually green in color, and feed chiefly upon
   fruits.
   [1913 Webster]

   Note: The common iguana (Iguana tuberculata) of the West
         Indies and South America is sometimes five feet long.
         Its flesh is highly prized as food. The horned iguana
         (Iguana cornuta) has a conical horn between the eyes.
         [1913 Webster]

WordNet (r) 3.0 (2006):

iguana
    n 1: large herbivorous tropical American arboreal lizards with a
         spiny crest along the back; used as human food in Central
         America and South America [syn: common iguana, iguana,
         Iguana iguana]