| Onatah | Woman | Native American - Iroquois Names |
| Onawa | Woman | Native American Names |
| Ondelette | Woman | French Names |
| Ondina | Woman | Spanish Names |
| Ondine | Woman | French Names |
| Ondre | Man | American Names |
| Ondrea | Unisex | Slavic Names |
| Oneida | Woman | Native American Names |
| Onelia | Woman | Spanish Names |
| Onelio | Man | Spanish Names |
| Onella | Woman | Hungarian Names |
| Oni | Woman | Native American Names |
| Onika | Woman | African - Igbo/West Africa Names |
| Onni | Man | Scandinavian Names |
| Onnika | Woman | Scandinavian Names |
| Onofre | Man | Spanish Names |
| Onofrio | Man | Greek Names |
| Onslow | Man | Arabic Names |
| Ontibile | Woman | African - Botswana Names |
| Onufry | Woman | Polish Names |