Source : Webster's Revised Unabridged Dictionary (1913)

Rambutan \Ram*bu"tan\, n. [Malay ramb[=u]tan, fr. rambut hair of
   the head.] (Bot.)
   A Malayan fruit produced by the tree {Nephelium lappaceum},
   and closely related to the litchi nut. It is bright red, oval
   in shape, covered with coarse hairs (whence the name), and
   contains a pleasant acid pulp. Called also {ramboostan}.

Source : WordNet®

rambutan
     n 1: Malayan tree bearing spiny red fruit [syn: {rambotan}, {rambutan
          tree}, {Nephelium lappaceum}]
     2: pleasantly acid bright red oval Malayan fruit covered with
        soft spines [syn: {rambotan}]