Thia can be a short form of names like Cynthia or Althea and also recalls Greek Theia, meaning goddess or divine.
Thia draws from one of the oldest and most luminous sources in the Western imagination: Greek mythology. Theia (also spelled Thia) was a Titaness, daughter of Uranus and Gaia, and one of the twelve original Titans who preceded the Olympian gods. Her name derives from the Greek "theia," meaning "divine" or "goddess," and she was specifically associated with light, shining, and the gleam of precious metals.
She was the mother, with her brother Hyperion, of Helios (the Sun), Selene (the Moon), and Eos (the Dawn) — making her, in a sense, the grandmother of all earthly light. 5 billion years ago, with the resulting debris coalescing into the Moon. This giant-impact hypothesis, now broadly accepted in planetary science, means that Theia is the name of the cosmic event that gave us our Moon — a staggering mythological coincidence that scientists embraced deliberately.
The name thus spans the distance from ancient Greek religious imagination to cutting-edge astrophysics. As a given name, Thia functions beautifully as both a standalone name and as a nickname for Cynthia, Dorothea, or Matthia. Its two-syllable lightness, ending in the open vowel "ah," gives it an airy, celestial quality entirely consistent with its mythological meaning. It has seen growing use among parents drawn to Greek mythology names that feel genuinely ancient rather than recently invented — a name that whispers of light and divine origin.