The Collaborative International Dictionary of English v.0.48:

Grison \Gri"son\, n. [F., fr. grison gray, gray-haired, gris
   gray. See Gris.] (Zool.)
   (a) A South American animal of the family Mustelidae
       (Galictis vittata). It is about two feet long,
       exclusive of the tail. Its under parts are black. Also
       called South American glutton.
   (b) A South American monkey (Lagothrix infumatus), said to
       be gluttonous.
       [1913 Webster]

WordNet (r) 3.0 (2006):

grison
    n 1: carnivore of Central America and South America resembling a
         weasel with a greyish-white back and dark underparts [syn:
         grison, Grison vittatus, Galictis vittatus]