Here are some synonyms for serene:
* Tranquil
* Peaceful
* Calm
* Quiet
* Composed
* Placid
* Unruffled
* Still
Examples of usage:
* "The serene beauty of the mountain lake was breathtaking."
* "She maintained a serene demeanor despite the chaos around her."
* "The music had a serene and soothing effect."
Origin:
The word "serene" comes from the Latin word "serēnus," meaning "clear, bright, calm."