O'Niall is a variant of the Irish surname O'Neal, which itself derives from the Gaelic Ó Néill, meaning "descendant of Neil." The name Neil (Irish Niall) is of disputed etymology, possibly from the Old Celtic root nītu- meaning "fury, passion" or the Old Irish word nia meaning "hero." Another proposed derivation links it to Old Irish nél ("cloud").
The O'Neills were a powerful Gaelic dynasty in Ireland, with roots tracing back to Niall of the Nine Hostages, a semi-legendary 5th-century high king. The surname spread worldwide through Irish emigration, especially to the United States, Canada, Australia, and the United Kingdom, during the 19th and 20th centuries. Variants like O'Niall, O'Neill, and Ó Néill reflect anglicization differences. According to historical records, the O'Niall spelling is less common but still found in some families from counties such as Cork and Waterford.
- Meaning: Variant of O'Neal (descendant of Neil)
- Origin: Irish
- Type: Surname
- Usage: Principally Ireland and among the Irish diaspora
Sources: Forebears — oniall