The Collaborative International Dictionary of English v.0.48:

Happy \Hap"py\ (h[a^]p"p[y^]), a. [Compar. Happier
   (-p[i^]*[~e]r); superl. Happiest.] [From Hap chance.]
   1. Favored by hap, luck, or fortune; lucky; fortunate;
      successful; prosperous; satisfying desire; as, a happy
      expedient; a happy effort; a happy venture; a happy omen.
      [1913 Webster]

            Chymists have been more happy in finding experiments
            than the causes of them.              --Boyle.
      [1913 Webster]

   2. Experiencing the effect of favorable fortune; having the
      feeling arising from the consciousness of well-being or of
      enjoyment; enjoying good of any kind, as peace,
      tranquillity, comfort; contented; joyous; as, happy hours,
      happy thoughts.
      [1913 Webster]

            Happy is that people, whose God is the Lord. --Ps.
                                                  cxliv. 15.
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            The learned is happy Nature to explore,
            The fool is happy that he knows no more. --Pope.
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   3. Dexterous; ready; apt; felicitous.
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            One gentleman is happy at a reply, another excels in
            a in a rejoinder.                     --Swift.
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   Happy family, a collection of animals of different and
      hostile propensities living peaceably together in one
      cage. Used ironically of conventional alliances of persons
      who are in fact mutually repugnant.

   Happy-go-lucky, trusting to hap or luck; improvident;
      easy-going. "Happy-go-lucky carelessness." --W. Black.
      [1913 Webster]

WordNet (r) 3.0 (2006):

happy-go-lucky
    adj 1: cheerfully irresponsible; "carefree with his money";
           "freewheeling urban youths"; "had a harum-scarum youth"
           [syn: carefree, devil-may-care, freewheeling,
           happy-go-lucky, harum-scarum, slaphappy]