Caitlin is the Irish form of Catherine, which reached Ireland through the Old French Cateline; Catherine itself is usually traced to the Greek katharos and read as "pure". The Irish pronunciation is closer to Kathleen, but American parents adopted the English reading "Kate-lin" and spawned a whole family of spellings. Caitlin ranked number 76 among US girls in 2000, the tail end of a boom that began in the 1980s, but it dropped out of the top 1000 in 2016 and sits at number 2333 in 2025.