eq ‧ ua ‧ nim ‧ i ‧ ty /ˌiːkwəˈnɪməti, ˌiːkwəˈnɪmɪti, ˌekwə-/ BrE AmE noun [uncountable]
[ Date: 1600-1700 ; Language: Latin ; Origin: aequanimitas , from aequo animo 'with level mind' ]
formal calmness in the way that you react to things, which means that you do not become upset or annoyed:
He received the news with surprising equanimity.