a calm state of mind
equanimity - calmness
If you have ‘equanimity’ then you are able to deal with stressful or difficult situations without losing your composure or breaking down. It is a formal word that has positive connotations, as if you have equanimity then life and the challenges it brings are much easier to bear.
I thought Alex would be upset by the bad news, but he absorbed it with surprising equanimity.
The trauma of that harrowing experience a few years ago really affected Diane. Only now is she regaining some of her equanimity.
David is brilliant at delivering results under pressure. Nothing seems to be able to disturb his equanimity.