Serenity comes from the Latin serenitas, meaning "peace" or "calm." The English word itself was first used as a personal name in the late 20th century, joining the wave of virtue names alongside Trinity, Destiny, and Harmony.
Serenity entered the U.S. top 100.
Serenity does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Serenity reduce to 7, The Seeker. This is a traditional interpretive system, not a factual claim about the name.