The Collaborative International Dictionary of English v.0.48:

Mrs \Mrs.\
   The customary abbreviation of Mistress or Missess when used
   as a title of courtesy, in writing and printing; as, Mrs.
   Clinton is commonly called by her full name, Hillary Rodham
   Clinton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Mrs.
    n 1: a form of address for a married woman [syn: Mrs, Mrs.]