Cynthia is from the Greek Kynthia — "woman of Mount Cynthus," the mountain on Delos where Artemis was born.
Featured in Propertius's Elegies (the poet's beloved was Cynthia).
Cynthia 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 Cynthia reduce to 8, The Visionary. This is a traditional interpretive system, not a factual claim about the name.