| Obed | | O-bed (English) | Biblical, Biblical Latin, Biblical Greek | |
| Oceanus | | - | Greek Mythology (Latinized) | |
| Odysseus | | o-DIS-ee-əs (English) | Greek Mythology | |
| Oedipus | | ED-i-pəs (English), EED-i-pəs (English) | Greek Mythology (Latinized) | |
| Oenone | | - | Greek Mythology (Latinized) | |
| Oidipous | | - | Greek Mythology | |
| Oinone | | - | Greek Mythology | |
| Okeanos | | - | Greek Mythology | |
| Olympia | | - | Greek, Slovak | |
| Olympias | | - | Ancient Greek | |
| Olympiodoros | | - | Ancient Greek | |
| Olympos | | - | Ancient Greek | |
| Omiros | | - | Greek | |
| Onesimos | | - | Ancient Greek, Biblical Greek | |
| Onesiphoros | | - | Ancient Greek, Biblical Greek | |