The Collaborative International Dictionary of English v.0.48:

Fortunate \For"tu*nate\ (?; 135), a. [L. fortunatus, p. p. of
   fortunare to make fortunate or prosperous, fr. fortuna. See
   Fortune, n.]
   1. Coming by good luck or favorable chance; bringing some
      good thing not foreseen as certain; presaging happiness;
      auspicious; as, a fortunate event; a fortunate concurrence
      of circumstances; a fortunate investment.
      [1913 Webster]

   2. Receiving same unforeseen or unexpected good, or some good
      which was not dependent on one's own skill or efforts;
      favored with good forune; lucky.

   Syn: Auspicious; lucky; prosperous; successful; favored;
        happy.

   Usage: Fortunate, Successful, Prosperous. A man is
          fortunate, when he is favored of fortune, and has
          unusual blessings fall to his lot; successful when he
          gains what he aims at; prosperous when he succeeds in
          those things which men commonly desire. One may be
          fortunate, in some cases, where he is not successful;
          he may be successful, but, if he has been mistaken in
          the value of what he has aimed at, he may for that
          reason fail to be prosperous.
          [1913 Webster]

WordNet (r) 3.0 (2006):

fortunate
    adj 1: having unexpected good fortune; "other, less fortunate,
           children died"; "a fortunate choice" [ant: unfortunate]
    2: supremely favored; "golden lads and girls all must / like
       chimney sweepers come to dust" [syn: fortunate, golden]
    3: presaging good fortune; "she made a fortunate decision to go
       to medical school"; "rosy predictions" [syn: fortunate,
       rosy]