The Collaborative International Dictionary of English v.0.48:

Orang-outang \O*rang"-ou*tang`\, Orang-utan \O*rang"-u*tan`\, n.
   [Malayan [=o]rang [=u]tan, i. e., man of the woods; [=o]rang
   man + [=u]tan a forest, wood, wild, savage.] (Zool.)
   An arboreal anthropoid ape (Pongo pygmaeus, formerly Simia
   satyrus), which inhabits Borneo and Sumatra. Often called
   simply orang. It is now an endangered species. [Written
   also orangutan, orangutang, orang-utan, ourang-utang,
   and oran-utan.]
   [1913 Webster +PJC]

   Note: It is over four feet high, when full grown, and has
         very long arms, which reach nearly or quite to the
         ground when the body is erect. Its color is reddish
         brown. In structure, it closely resembles man in many
         respects.
         [1913 Webster]

WordNet (r) 3.0 (2006):

orangutang
    n 1: large long-armed ape of Borneo and Sumatra having arboreal
         habits [syn: orangutan, orang, orangutang, Pongo
         pygmaeus]