adjective
serene
suh-REEN/səˈriːn/
Calm, peaceful, and untroubled.
The older woman looks serene beside the still pond.

Etymology
Latin serenus described clear, unclouded weather and also figurative tranquility. Applied to a person or character, that fair-weather image conveys a calm, unruffled state.
In context
Sarah Whitmore looked like she was sleeping. Her face was peaceful, almost serene.
More examples
- The lake looks serene in the early morning light.
- His serene expression gives no hint of worry.
- The garden feels serener once the visitors leave.
Forms
serene · serener · serenest
serenity noun — The state of being calm and untroubled.
serenely adverb — In a calm and untroubled manner.