American buffalo (5)
I believe the answer is:
bison
'american buffalo' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for bison that I've seen before include "Ox-like ruminant" , "It's a buffalo in America" , "Large shaggy wild ox" , "North American buffalo" , "Shaggy-haired wild ox" .)