The Collaborative International Dictionary of English v.0.48:

Dugong \Du*gong"\ (d[.u]*g[o^]g"), n. [Malayan d[=u]y[=o]ng, or
   Javan. duyung.] (Zool.)
   An aquatic herbivorous mammal (Halicore dugong), of the
   order Sirenia, allied to the manatee, but with a bilobed
   tail. It inhabits the Red Sea, Indian Ocean, East Indies, and
   Australia. [Written also duyong.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

dugong
    n 1: sirenian tusked mammal found from eastern Africa to
         Australia; the flat tail is bilobate [syn: dugong,
         Dugong dugon]