Rare diminutive, possibly a pet form of names like Felicity or a Southern American invention.
Fallie is a rare diminutive, possibly connected to Felicity or another name beginning with the Fal- sound, and it may also reflect regional or family invention. That uncertain background is typical of many pet-form names that move into wider use by charm rather than pedigree.
It feels soft, affectionate, and lightly old-fashioned. In contemporary naming, Fallie has the kind of modest sweetness that can make a rare name feel approachable. It sounds friendly and a little nostalgic, with the texture of a nickname that has become independent.
The name is simple, but not plain. Fallie feels like a name that favors warmth over formality, and that gives it a distinctive emotional register.