The Collaborative International Dictionary of English v.0.48:

Gaucho \Gau"cho\ (gou"ch[-o]), n., pl. Gauchos (gou"ch[-o]z)
   [Sp.]
   One of the native inhabitants of the South American pampas,
   of Spanish-American descent. They live mostly by rearing
   cattle. Hence, a South American cowboy, especially on the
   pampas.
   [1913 Webster]

   2. A member of an Indian population, somewhat affected by
      Spanish blood, in the archipelagoes off the Chilean coast.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

gaucho
    n 1: a cowboy of the South American pampas