Caelin, an Anglicized variant of the Irish Gaelic Caolán—diminutive of caol “slender” or “narrow”—has been embraced as a unisex name within Anglo-American usage, its formal structure and balanced phonetic pattern (KAY-lin, /keɪleɪn/) reflecting both linguistic economy and melodic symmetry. As an analytical exercise in onomastics, its incidence in the United States has remained modest yet consistent since its first recorded appearance in Social Security Administration data in 1992 (five births, rank 764), with rank values oscillating between the mid-700s and high-900s and peaking at eighteen occurrences in 2003 (rank 810) before returning to five births in 2022 (rank 938), thereby illustrating a stable niche presence. This restrained adoption signifies Caelin’s appeal to parents seeking a name that combines traditional Gaelic roots with contemporary unisex sensibilities, allowing for cultural resonance without widespread popularity. The name’s enduring rarity, coupled with its scholarly etymological provenance, ensures its status as a designation of understated distinction within the broader tapestry of Anglo-American naming conventions.