| Oakes | Unisex | English Names |
| Oakley | Unisex | English Names |
| Obedience | Woman | English Names |
| Ode | Unisex | English Names |
| Odell | Unisex | English Names |
| Odo | Man | English Names |
| Ogden | Man | English Names |
| Oliva | Woman | English Names |
| Olive | Woman | English Names |
| Oliver | Man | English Names |
| Olivera | Woman | English Names |
| Olivia | Woman | English Names |
| Ollie | Man | English Names |
| Onyx | Unisex | English Names |
| Orchid | Unisex | English Names |
| Orde | Man | English Names |
| Ordell | Unisex | English Names |
| Ormand | Man | English Names |
| Orrick | Man | English Names |
| Orsen | Man | English Names |