Source : Webster's Revised Unabridged Dictionary (1913)

Happiness \Hap"pi*ness\, n. [From {Happy}.]
   1. Good luck; good fortune; prosperity.

            All happiness bechance to thee in Milan! --Shak.

   2. An agreeable feeling or condition of the soul arising from
      good fortune or propitious happening of any kind; the
      possession of those circumstances or that state of being
      which is attended enjoyment; the state of being happy;
      contentment; joyful satisfaction; felicity; blessedness.

   3. Fortuitous elegance; unstudied grace; -- used especially
      of language.

            Some beauties yet no precepts can declare, For
            there's a happiness, as well as care. --Pope.

   Syn: {Happiness}, {Felicity}, {Blessedness}, {Bliss}.

   Usage: Happiness is generic, and is applied to almost every
          kind of enjoyment except that of the animal appetites;
          felicity is a more formal word, and is used more
          sparingly in the same general sense, but with elevated
          associations; blessedness is applied to the most
          refined enjoyment arising from the purest social,
          benevolent, and religious affections; bliss denotes
          still more exalted delight, and is applied more
          appropriately to the joy anticipated in heaven.

                O happiness! our being's end and aim! --Pope.

                Others in virtue place felicity, But virtue
                joined with riches and long life; In corporal
                pleasures he, and careless ease.  --Milton.

                His overthrow heaped happiness upon him; For
                then, and not till then, he felt himself, And
                found the blessedness of being little. --Shak.

Source : WordNet®

happiness
     n 1: state of well-being characterized by emotions ranging from
          contentment to intense joy [syn: {felicity}] [ant: {unhappiness}]
     2: emotions experienced when in a state of well-being [ant: {sadness}]