equanimity |ˌēkwəˈnimitē; ˌekwə-|
noun
mental calmness, composure, and evenness of temper, esp. in a difficult situation : he accepted both the good and the bad with equanimity.
ORIGIN early 17th century — also in the sense 'fairness, impartiality' — from Latin aequanimitas, from aequus ‘equal’ + animus ‘mind.’