| Ockvilly | A dweller of the rocky meadow. |
| Offede | A name meaning peace or harmony. |
| Oiddii | A name meaning a small treasure. |
| Oissine | Derived from Gaelic, meaning fawn. |
| Okindu | A name of African origin meaning sun. |
| Okitha | A name meaning a bright, shining star. |
| Okithma | A name meaning one who is very wise. |
| Ol | Legendary son of olwydd |
| Olajuwon | A name meaning honor is wealth to me. |
| Olamilekan | My wealth is growing |
| Oleena | A name meaning a bright, shining light. |
| Olimpiades | A name meaning of the Olympic games. |
| Olivander | Derived from the olive tree wood. |
| Oliwer | A variant of the name Oliver. |
| Oliwier | A Polish variation of Oliver. |
| Ollen | Young warrior, a Gaelic name meaning youthful strength |
| Ollivander | Famous warrior, a French name meaning renowned fighter |
| Olmo | Elm tree, a Spanish name meaning strong and resilient |
| Olowin | A friend of the forest spirits. |
| Olu | God is my peace, a Yoruba name meaning divine calm |
| Omalmith | A name meaning a noble protector. |
| Ometh | One who is a faithful follower. |
| Omiru | One who is a shining star light. |
| Omishka | A name meaning a gift of love. |
| Omitha | One who is full of light. |
| Omithma | The soul of the sacred sound. |
| Omkarmurty | Embodiment of the Om sound. |
| Omni | All-powerful, a Latin name meaning universal power |
| Ond | A name meaning wave or water. |
| Onel | A name meaning light of God. |
| Onochie | God is my strength, a Nigerian name meaning divine support |
| Ontario | Beautiful place, a Native American name meaning lovely location |
| Optimus | Best, a Latin name meaning superior or excellent |
| Opus | Work, a Latin name meaning creation or achievement |
| Ordmaer | A noble and golden ruler. |
| Orev | God is my shepherd, a Hebrew name meaning divine guidance |
| Orie | God is my light, a Nigerian name meaning divine illumination |
| Orley | Famous meadow, a French name meaning renowned pasture |
| Orlo | Famous hill, a Russian name meaning renowned elevation |
| Orrie | Famous warrior, a Gaelic name meaning renowned fighter |