Probably a variant of Cynthia, from Mount Kynthos, an epithet of the goddess Artemis.
Cynetha is probably a variant of Cynthia, ultimately from Mount Kynthos, an epithet associated with the goddess Artemis. That mythological background gives the name a classical pedigree, linking it to moonlit imagery, Greek place-naming, and the long afterlife of Artemis in Western naming.
Cynetha keeps that lineage visible while reshaping it into something more unusual and individualized. Because it is a variant rather than a standard form, Cynetha has the feeling of a name that has traveled through time and spelling changes. It sounds elegant but not commonplace, and its difference from Cynthia makes it stand apart without losing the mythic reference.
This kind of altered classical name often feels both learned and inventive. Cynetha has that balance: rooted in antiquity, but distinct enough to feel personal and modern.