The Collaborative International Dictionary of English v.0.48:

White slave \White slave\
   A woman held in involuntary confinement for purposes of
   prostitution; loosely, any woman forced into unwilling
   prostitution.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

white slave
    n 1: a woman sold into prostitution

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "white slave":
   B-girl, Cyprian, Paphian, call girl, daughter of joy,
   erring sister, fallen woman, fille de joie, harlot, hooker,
   hustler, meretrix, painted woman, poule, prostitute, scarlet woman,
   stew, streetwalker, unfortunate woman, whore