Cassidy is from the Irish surname Ó Caiside — from casideach ("curly-haired" or "clever"). Her 2023 memoir Enough was a New York Times bestseller. The story of her posthumous fame is one of the most-cited in 21st-century music history. David Cassidy is male (The Partridge Family). Hopalong Cassidy is male (1935 character). Butch Cassidy is male (Sundance Kid partner).
Cassidy 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 Cassidy reduce to 8, The Visionary. This is a traditional interpretive system, not a factual claim about the name.