The Collaborative International Dictionary of English v.0.48:

Negress \Ne"gress\, n.; pl. Negresses. [Cf. F. n['e]grese,
   fem. of n['e]gre a negro. See Negro.]
   A black woman; a female negro.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Negress
    n 1: a Black woman or girl