noun (n)

• steadiness of mind under stress(noun.attribute)

  Example:
  He accepted their problems with composure and she with equanimity.
  

  Synonym:
  calm, calmness, composure
  Antonym:
  discomposure
  

  source: wordnet30
• Evenness of mind; that calm temper or firmness of mind which is not easily elated or depressed; patience; calmness; composure; as, to bear misfortunes with equanimity.(noun)

  source: webster1913