/ ˌekwəˈnɪməti; NAmE / noun
[ U ] ( formal ) a calm state of mind which means that you do not become angry or upset, especially in difficult situations :
She accepted the prospect of her operation with equanimity .
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WORD ORIGIN
early 17th cent. (also in the sense fairness, impartiality): from Latin aequanimitas , from aequus equal + animus mind.