The Collaborative International Dictionary of English v.0.48:

Happiness \Hap"pi*ness\, n. [From Happy.]
   1. Good luck; good fortune; prosperity.
      [1913 Webster]

            All happiness bechance to thee in Milan! --Shak.
      [1913 Webster]

   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 with enjoyment; the state of being
      happy; contentment; joyful satisfaction; felicity;
      blessedness.
      [1913 Webster]

   3. Fortuitous elegance; unstudied grace; -- used especially
      of language.
      [1913 Webster]

            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.
          [1913 Webster]

                O happiness! our being's end and aim! --Pope.
          [1913 Webster]

                Others in virtue place felicity,
                But virtue joined with riches and long life;
                In corporal pleasures he, and careless ease.
                                                  --Milton.
          [1913 Webster]

                His overthrow heaped happiness upon him;
                For then, and not till then, he felt himself,
                And found the blessedness of being little.
                                                  --Shak.
          [1913 Webster]

WordNet (r) 3.0 (2006):

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

The Devil's Dictionary (1881-1906):

HAPPINESS, n.  An agreeable sensation arising from contemplating the
misery of another.