noun (n)

• the quality of being cheerful and dispelling gloom(noun.attribute)

  Example:
  Flowers added a note of cheerfulness to the drab room.
  

  Synonym:
  cheer, sunniness, sunshine
  Antonym:
  uncheerfulness
  

  source: wordnet30
• a feeling of spontaneous good spirits(noun.feeling)

  Example:
  His cheerfulness made everyone feel better.
  

  Synonym:
  blitheness
  Antonym:
  cheerlessness, uncheerfulness
  

  source: wordnet30
• Good spirits; a state of moderate joy or gayety; alacrity.(noun)

  source: webster1913