Diminutive of Dahlia or Dallas, a playful pet form used as a given name.
Dallie has the feeling of a name that was loved before it was official — a pet name that slipped its leash and became the real thing. It most likely functions as a diminutive of Dale, which comes from the Old English and Old Norse "dæl" or "dalr," both meaning a valley. Valley names carry a quiet, sheltered quality in English culture: a dale is a place of pastoral refuge, a fold in the landscape where things grow protected from wind.
The -ie suffix does what diminutive suffixes have always done in English names — it draws the name close, makes it affectionate, keeps it human. Dallie could also be read as a variation on Dahlia, the flower name derived from the Swedish botanist Anders Dahl. Dahlias, with their complex layered petals, have been associated with elegance, change, and inner strength — not a bad set of associations for a name to carry quietly.
The phonetic similarity means Dallie sits at a comfortable intersection of several traditions without being identical to any of them. What makes Dallie interesting today is precisely its rarity. It has the soft ending and the double-letter warmth that have made names like Callie, Hallie, and Sallie perennially beloved, but without the overexposure those names have sometimes suffered. It sounds like it belongs in a Southern novel or a family with a talent for names that are simultaneously informal and memorably distinct.