The Collaborative International Dictionary of English v.0.48:

Gentlewoman \Gen"tle*wom`an\, n.; pl. Gentlewomen.
   [1913 Webster]
   1. A woman of good family or of good breeding; a woman above
      the vulgar. --Bacon.
      [1913 Webster]

   2. A woman who attends a lady of high rank. --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

gentlewoman
    n 1: a woman of refinement; "a chauffeur opened the door of the
         limousine for the grand lady" [syn: dame, madam,
         ma'am, lady, gentlewoman]

Moby Thesaurus II by Grady Ward, 1.0:

65 Moby Thesaurus words for "gentlewoman":
   Eve, Frau, abigail, amah, archduchess, au pair girl, ayah,
   baroness, betweenmaid, biddy, chambermaid, chaperon, companion,
   cook, countess, dame, daughter of Eve, distaff, domina, donna,
   dowager, duchess, duenna, femme, femme de chambre,
   fille de chambre, frow, girl, grand duchess, handmaid, handmaiden,
   hired girl, housemaid, khanum, kitchenmaid, lady, lady-help,
   lady-in-waiting, lass, live-in maid, live-out maid, maid,
   maidservant, marchioness, margravine, matron, milady, noblewoman,
   nursemaid, parlormaid, peeress, scullery maid, servant girl,
   servitress, soubrette, squaw, tweeny, upstairs maid, viscountess,
   vrouw, wahine, waiting maid, weaker vessel, wench, woman



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

GENTLEWOMAN. This word is unknown to the law in the United States, and is
but little used. In England. it was, formerly, a good addition of the state
or degree of a woman. 2 Inst. 667.