Cassidie

Cassidie is a modern English spelling variant of the Irish surname Cassidy. The surname itself is derived from the Gaelic 'Ó Caiside', meaning 'descendant of Caiside'. Caiside is a personal name meaning 'curly-haired'. While originally a surname, it began to be used as a given name, particularly for girls, in the late 20th century, following a trend of feminizing surnames or creating new spellings for existing names.

The popularity of Cassidy as a given name, and subsequently its variants like Cassidie, increased in English-speaking countries, especially in North America. The 'ie' ending is a common way to feminize or soften names, giving it a more delicate feel than the original surname. It remains a less common spelling than Cassidy, contributing to its unique appeal.