Ó Cadhain is a surname of Irish origin, commonly associated with the Gaelic language. It is derived from the word "cadh," meaning "battle" or "warrior." The name is often linked to the Connacht region of Ireland, where many families with this surname can be found. One notable figure with this surname is Máirtín Ó Cadhain, a prominent Irish writer and playwright. He was known for his contributions to Irish literature, particularly in the Irish language. His works often explored themes of identity, culture, and the complexities of life in Ireland.