The Collaborative International Dictionary of English v.0.48:

Bison \Bi"son\ (b[imac]"s[o^]n; 277), n. [L. bison, Gr. bi`swn,
   a wild ox; akin to OHG. wisunt, wisant, G. wisent, AS.
   wesend, Icel. v[imac]sundr: cf. F. bison.] (Zool.)
   (a) The aurochs or European bison.
   (b) The American bison buffalo (Bison Americanus), a large,
       gregarious bovine quadruped with shaggy mane and short
       black horns, which formerly roamed in herds over most of
       the temperate portion of North America, but by 1900 was
       restricted to very limited districts in the region of the
       Rocky Mountains, and was almost hunted to extinction.

   Note: Efforts at conservation of the American bison resulted
         in setting aside several reserves, and by 1990 a few
         stable herds were established, numbering from hundreds
         to thousands, roaming certain public areas, such as
         Yellowstone Park, some reserves in Canada, and some
         private reserves. Some bison are kept as range animals
         for food, and the American bison has been bred with
         domestic cattle to form a cross called the beefalo.
         The American bison is commonly (though improperly)
         called a buffalo; an image of the bison appeared on the
         inverse of the U. S. five-cent coin (nickel) from 1913
         to 1937, and that coin was referred to as the buffalo
         nickel.
         [1913 Webster +PJC]