Heilyn (HAY-lin; /ˈheɪ.lɪn/) is a feminine given name of modern Welsh provenance, distinguished by the confluence of Old English haeg (‘hay clearing’) and the Welsh llyn (‘lake’), a synthesis that articulates a pastoral resonance within an Anglo-Welsh onomastic framework. Although unattested in medieval Celtic records, its phonological structure and semantic underpinnings evoke both agrarian landscapes and contemporary linguistic hybridity, positioning it as a symbol of cultural nuance rather than widespread adoption. Social Security Administration figures chart a modest yet steady usage in the United States since the late 2000s—ten occurrences in 2024 (rank 940), a peak of thirteen in 2023, and annual frequencies seldom exceeding fifteen—which underscores its appeal to parents who favor names of measured rarity, scholarly depth, and subtle resonance with both Anglo-American and Celtic traditions.