Source : Webster's Revised Unabridged Dictionary (1913)

Opossum \O*pos"sum\, n. [Of N. American Indian origin.]
   (Zo["o]l.)
   Any American marsupial of the genera {Didelphys} and
   {Chironectes}. The common species of the United States is
   {Didelphys Virginiana}.

Source : WordNet®

opossum
     n 1: small furry Australian arboreal marsupials having long
          usually prehensile tails [syn: {phalanger}, {possum}]
     2: nocturnal arboreal marsupial having a naked prehensile tail
        found from southern North America to northern South
        America [syn: {possum}]