The Collaborative International Dictionary of English v.0.48:

Crees \Crees\ (kr[=e]z), n. pl.; sing. Cree. (Ethnol.)
   An Algonquin tribe of Indians, inhabiting a large part of
   British America east of the Rocky Mountains and south of
   Hudson's Bay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Cree
    n 1: a member of an Algonquian people living in central Canada
    2: the Algonquian language spoken by the Cree