A spelling variant of Cassidy, from an Irish surname meaning curly-haired or clever-haired.
Kassidy is a modern spelling of Cassidy, a name that began as an Irish surname. Cassidy comes from O Caiside, generally linked to the Gaelic personal name Caiside, which is associated with curly hair and, by extension, a lively or distinctive appearance. The spelling with K is a very late development, part of the modern tendency to reshape traditional names with new initials or phonetic spellings.
That means Kassidy is ancient in root but contemporary in presentation, which is exactly why it feels both familiar and fresh. The older surname carried history through Ireland, while the broader Cassidy family of names entered popular culture through figures and references such as Butch Cassidy. As a first name, however, Cassidy and then Kassidy rose mainly in the late twentieth century, especially in North America, where surname-style names became fashionable for girls.
The K spelling made the name feel even more youthful and individualized, and bearers such as Olympic diver Kassidy Cook helped make it visible in real life rather than only on birth announcements. Over time, Kassidy has shifted from trendy and slightly spunky to a more settled modern classic of its era. It still carries a cheerful, bright energy, but its Irish surname ancestry gives it more depth than its glossy spelling first suggests.