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]