Latin placiditās (“mildness, placidity”).
placidity (usually uncountable, plural placidities)
- The state of being placid; peacefulness.
1815, Jane Austen, Emma, volume III, chapter 10:
- 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.