Cassidy is a surname name derived from an Irish surname and ultimately from the Gaelic given name Caiside, meaning "clever" or "curly-haired."
The name Caiside comes from the Irish word element cas.
Cassidy was the 244th most popular name for girls born in the United States in 2009.
It first appeared among the 1,000 most popular names for American girls in 1981.
Kassidy, an alternate spelling, was ranked as the 443rd most popular name for girls in 2009.