| Name | Gender | Pronounced | Usage | Popularity |
|---|---|---|---|---|
| Ona (1) | - | Lithuanian | ||
| Ona (2) | - | Catalan | ||
| Ondina | - | Portuguese, Italian | ||
| Onesimos | - | Ancient Greek, Biblical Greek | ||
| Onesiphoros | - | Ancient Greek, Biblical Greek | ||
| Oni | - | Western African, Yoruba | ||
| Onisim | - | Russian (Rare) | ||
| Onyeka | - | Western African, Igbo | ||
| Onyekachi | - | Western African, Igbo | ||
| Onyekachukwu | - | Western African, Igbo | ||
| Opeyemi | - | Western African, Yoruba | ||
| Orabela | o-rah-BE-lah | Esperanto | ||
| Orazio | - | Italian | ||
| OrbÁN | - | Hungarian | ||
| Orfeo | - | Italian, Spanish |