placidity

noun

1. (uncountable, usually)The state of being placid; peacefulness.

   “And how could she bear such behaviour! Composure with a witness! to look on, while repeated attentions were offering to another woman, before her face, and not resent it.—That is a degree of placidity, which I can neither comprehend nor respect.”

   “Thus, in rapid succession, passed the thoughts of Rosilia, who, endeavouring to assume placidity, once more essayed to express her thanks to Mrs. Melbourne for her kind attentions,[…]”

   “The swift and indifferent placidity of that look troubled me.”