The phrase "a serenity" is correct and usable in written English.
You can use it to describe a peaceful, calm, or tranquil atmosphere. For example, "The sun was setting, and a serenity settled over the beach."
Even a serenity fountain.
He conveyed a serenity, optimism and strength that touched hearts.
Mr. Goldwyn also has a serenity unusual for Hollywood.
I'm louder, whereas Kevin has a serenity, which I find very endearing.
There is a serenity and calm that runs through its streets.
But "The Sleeping Beauty" beams a serenity that at times seems unrelenting.
These have an almost formal elegance and a serenity that sets them apart from the others.
"There is definitely a serenity in his life now," the French writer Olivier Royant told me.
"There was a serenity, a calm confidence that I found unusually attractive," she said.
In among these lush rows, there is a serenity unique to Africa.
It has a serenity that belies the chaos and violence that killed the 58,000 soldiers who are remembered there.
