The Collaborative International Dictionary of English v.0.48:

Madame \Ma`dame"\, n.; pl. Mesdames. [F., fr. ma my (L. mea) +
   dame dame. See Dame, and cf. Madonna.]
   My lady; -- a French title formerly given to ladies of
   quality; now, in France, given to all married women.
   --Chaucer.
   [1913 Webster] Mad-apple

WordNet (r) 3.0 (2006):

madame
    n 1: title used for a married Frenchwoman