In the Irish language, the noun Grian means the Sun, and is grammatically feminine. While Grian's name literally means "the sun" in modern Irish, her name is derived from the Proto-Indo European word *gwher-, meaning "to be hot" or "to burn" rather than the derivations for sun in other Indo-European languages.
This word has scholars suspect that it is also the name of an Irish deity due to a hill in Limerick county in Ireland, Cnoc Gréine.
Cnoc Gréine is close to the hill of the goddess Áine, Cnoc Áine (Knockainy). Due to this relation scholars suspect that Grian is believed to be either the sister of Áine, another of Áine's manifestations, or possibly "Macha in disguise".