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]

Moby Thesaurus II by Grady Ward, 1.0:

117 Moby Thesaurus words for "happiness":
   Easy Street, acceptance, affluence, appropriateness, beatification,
   beatitude, becomingness, bed of roses, bewitchment, blessedness,
   bliss, blissfulness, blitheness, blithesomeness, brightness, cheer,
   cheerfulness, cheeriness, cheery vein, civility, cloud nine,
   clover, comfort, composure, content, contentedness, contentment,
   decency, decorousness, decorum, delectation, delight, ease,
   easy circumstances, ecstasy, ecstatics, elation, enchantment,
   enjoyment, entire satisfaction, eupeptic mien, euphoria,
   exaltation, exhilaration, exuberance, felicity, fitness,
   fittingness, fleshpots, fulfillment, gaiety, geniality,
   genteelness, gentility, gladness, gladsomeness, glee, good cheer,
   gracious life, gracious living, heaven, high spirits, hopefulness,
   intoxication, jollity, joy, joyance, joyfulness, joyousness,
   jubilation, lap of luxury, life of ease, loaves and fishes, luxury,
   meetness, optimism, overhappiness, overjoyfulness, paradise,
   peace of mind, pleasantness, pleasure, properness, propriety,
   prosperity, prosperousness, radiance, rapture, ravishment,
   reconcilement, reconciliation, resignation, rightness,
   rosy expectation, sanguine humor, sanguineness, satisfaction,
   security, seemliness, seventh heaven, success, suitability,
   sunniness, sunshine, the affluent life, the good life,
   thriving condition, transport, unalloyed happiness,
   upward mobility, urbanity, velvet, weal, wealth, welfare,
   well-being, winsomeness



The Devil's Dictionary (1881-1906):

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