Evenness of mind especially under stress. (Merriam – Webster)
Right disposition: Balance. (Merriam – Webster)
A calm mental state, especially after a shock or disappointment or in a difficult situation. (Cambridge Dictionary)
Mental or emotional stability or composure, especially under tension or strain; calmness; equilibrium. (Dictionary.com)
Calmness and composure, especially in a difficult situation. (Oxford Dictionaries)
Equanimity is a calm state of mind and attitude to life, so that you never lose your temper or become upset. (Collins Dictionary)
What is Equanimity?
Equanimity. Insight meditation centre.