Cecily is the English form of Cecilia — from the Latin caecus (blind) — the Roman gens Caecilia clan name. (Apple TV+ 2021-2023); The Bride Wore Boots (2024).
Cecily 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 Cecily reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.