The Collaborative International Dictionary of English v.0.48:

Doxy \Dox"y\, n.; pl. Doxies. [See Duck a pet.]
   A loose wench; a disreputable sweetheart. --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

doxy
    n 1: a woman who cohabits with an important man [syn:
         concubine, courtesan, doxy, paramour]