noun (n)

• the trait of remaining calm and seeming not to care; a casual lack of concern(noun.attribute)

  Synonym:
  indifference, nonchalance
  

  source: wordnet30
• a feeling of lack of concern(noun.feeling)

  Antonym:
  concern
  

  source: wordnet30
• Want of concern; absence of anxiety; freedom from solicitude; indifference.(noun)

  source: webster1913