The Collaborative International Dictionary of English v.0.48:

Mestizo \Mes*ti"zo\, n.; pl. Mestizos. [Sp. mestizo; akin to
   OF. mestis, F. m['e]tis; all fr. (assumed) LL. mixtitius, fr.
   L. mixtus mixed, p. p. of miscere to mix. See Mix, and cf.
   Mestee, M['e]tif, M['e]tis, Mustee.]
   The offspring of an Indian or a negro and a European or
   person of European stock. [Spanish America]
   [1913 Webster]

   Mestizo wool, wool imported from South America, and
      produced by mixed breeds of sheep.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mestizo
    n 1: a person of mixed racial ancestry (especially mixed
         European and Native American ancestry) [syn: mestizo,
         ladino]