The Collaborative International Dictionary of English v.0.48:

Mulatto \Mu*lat"to\, n.; pl. Mulattoes. [Sp. & Pg. mulato,
   masc., mulata, fem., of a mixed breed, fr. mulo mule, L.
   mulus. See Mule.]
   The offspring of a negress by a white man, or of a white
   woman by a negro, -- usually of a brownish yellow complexion.
   [1913 Webster]

WordNet (r) 3.0 (2006):

mulatto
    n 1: an offspring of a black and a white parent

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "mulatto":
   Cape Colored, Eurasian, cattalo, citrange, cross, crossbreed,
   griffe, half blood, half-bred, half-breed, half-caste, high yellow,
   hinny, hybrid, ladino, liger, mestee, mestiza, mestizo, metis,
   metisse, mixblood, mixed-blood, mongrel, mule, mustee, octoroon,
   plumcot, quadroon, quintroon, sambo, tangelo, tigon, zebrass,
   zebrule



Bouvier's Law Dictionary, Revised 6th Ed (1856):

MULATTO. A person born of one white and one black parent. 7 Mass. R. 88; 2
Bailey, 558.



The Devil's Dictionary (1881-1906):

MULATTO, n.  A child of two races, ashamed of both.