Kaci is a modern American spelling of Casey, which comes from the Irish surname Ó Cathasaigh and means "vigilant" or "watchful". The spelling with a K and an i fits the 1990s fashion for respelled unisex names such as Kasey and Kacey. Kaci peaked at number 952 in 2000, its only year inside the top 1000, and has slipped to number 2132 in 2025.