The Collaborative International Dictionary of English v.0.48:

Mangosteen \Man"go*steen\, Mangostan \Man"go*stan\, mangosteen
tree \mangosteen tree\n. [Malay mangusta, mangis.] (Bot.)
   A tree of the East Indies of the genus Garcinia (Garcinia
   Mangostana) with thick leathery leaves. The tree grows to
   the height of eighteen feet, and bears fruit also called
   mangosteen, of the size of a small apple, the pulp of which
   is very delicious food.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mangosteen tree
    n 1: East Indian tree with thick leathery leaves and edible
         fruit [syn: mangosteen, mangosteen tree, Garcinia
         mangostana]