O'Brien surname meaning

O’Brien is the anglicized form of Irish Ó Briain, meaning “descendant of Brian.” Brian was a medieval Gaelic personal name, and its deeper meaning is often discussed as “high” or “noble,” though that gloss belongs to the given name rather than directly to the surname. The apostrophe records the Gaelic prefix Ó, but American documents frequently dropped it, producing OBrien or Obrien. Different O’Brien families could descend from different men named Brian, so the patronymic does not prove one shared genealogy. Parent’s name is the direct, high-confidence type.