The Collaborative International Dictionary of English v.0.48:

Desperado \Des`per*a"do\, n.; pl. Desperadoes. [OSp.
   desperado, p. p. of desperar, fr. L. desperare. See
   Desperate.]
   A reckless, furious man; a person urged by furious passions,
   and regardless of consequence; a wild ruffian.
   [1913 Webster]

WordNet (r) 3.0 (2006):

desperado
    n 1: a bold outlaw (especially on the American frontier) [syn:
         desperado, desperate criminal]