Likely related to Olena or Helena forms, ultimately connected with light or torchlike brightness.
Olenna is a melodious elaboration of the ancient Greek name Helene, whose probable root is the word selene (moon) or, in an older interpretation, a pre-Greek word for 'torch' or 'bright one.' Helen of Troy, the most famous ancient bearer, made the name synonymous with legendary beauty and world-altering consequence — Homer's Iliad describes her as the face that launched a thousand ships. As the name traveled through Latin, Byzantine Greek, and then into the Romance languages, it spawned a vast family of variants: Elena, Elene, Eleanor, Lena, and eventually the softer, more lyrical Olenna.
The form Olenna gained significant cultural traction in the 2010s through the character Olenna Tyrell in George R. R. Martin's A Song of Ice and Fire and its HBO adaptation Game of Thrones.
Played with scene-stealing wit by Diana Rigg, the 'Queen of Thorns' gave the name an association with sharp intelligence, aristocratic poise, and devastating one-liners — a far cry from the passive beauty of the original Helen myth. It was a rare instance of a fantasy series genuinely refreshing a classical name. Outside of Westeros, Olenna has the warm, sun-drenched feel of Italian and Mediterranean femininity, sitting naturally alongside Sienna, Gianna, and Alessia. It is old enough to feel grounded and rare enough to feel distinctive — a combination that makes it increasingly appealing to parents who want something timelessly pretty without reaching for the overtly trendy.