composure       
noun [ U ] uk/kəmˈpəʊ.ʒər/ us/kəmˈpoʊ.ʒɚ/
 镇静,沉着,泰然自若
the feeling of being calm, confident, and in control
  I didn't want to lose my composure in front of her. 我不想在她面前失态。 
 Synonyms: calm calmnesscool (CALM) equanimity phlegm (CALMNESS) sangfroid