Variant of Carolyn, from Germanic Karl meaning 'free man' or 'strong.'
Carlyn is one of several variant spellings that emerged from the extraordinarily productive name-family of Caroline and Carolyn, which ultimately trace back to the masculine name Charles. Charles derives from the Germanic "karl," meaning "free man" or simply "man" in the sense of a full adult member of society — the same root that gives English the word "churl" and the Scandinavians their "Karl." The Latinized Carolus became Charlemagne's name in historical records; his daughter Carola was among the earliest feminine forms, and the name spread through European royal houses across the centuries.
Caroline in its various forms became enormously fashionable in eighteenth-century England, boosted by the Hanoverian queens Caroline of Ansbach (wife of George II) and Caroline of Brunswick (wife of George IV). By the nineteenth century it had thoroughly naturalized into English-speaking culture, and the twentieth century saw an explosion of variant spellings: Carolyn, Carolyne, Carolinn, and Carlyn, among others. These variants represent the American habit of personalizing familiar names through creative orthography, making each spelling feel slightly unique while preserving the phonetic inheritance.
Carlyn specifically has a clean, contemporary look — the dropped "o" gives it a more modern visual rhythm while preserving the sound of its roots. It peaked in American usage in the mid-twentieth century alongside its sister spellings, part of the broader Carol family that dominated girls' naming for decades. Today it has the appealing quality of a name that feels familiar and approachable without being common — carrying the historical weight of Charlemagne's lineage lightly, in comfortable everyday clothes.