| Ortona | Beautiful hill, an Italian name meaning lovely location |
| Ortwin | Spearhead, friend |
| Orvel | Derived from the golden city. |
| Orvon | Famous mountain, a Welsh name meaning renowned peak |
| Orwell | Derived from the surname of the English author George Orwell. |
| Oryon | Boundary, limit |
| Osca | A champion of the divine spear. |
| Oscon | Possibly derived from the Latin word 'os,' meaning mouth. |
| Oshadh | A name meaning medicinal herb. |
| Oshan | A name meaning calm or quiet. |
| Oshana | A name meaning bright light. |
| Oshen | A name meaning deep ocean blue. |
| Oshitha | A name meaning bright radiance. |
| Osiru | A name meaning divine spirit. |
| Oslo | Derived from the Old Norse words 'óss' and 'ló,' meaning sacred meadow. |
| Oslow | Meadow of the gods |
| Osmel | Derived from the Latin word 'os,' meaning mouth, and the suffix '-mel.' |
| Otey | Derived from the Old English word 'ot,' meaning fire. |
| Othon | Wealth and prosperity |
| Otten | A name meaning wealthy or rich. |
| Oukouaka | Derived from the Greek words 'oukos' and 'ouka,' meaning good and noble. |
| Ovindu | A name meaning a calm ocean wave. |
| Oahu | A place gathered together |
| Oberyn | A noble and brave spirit |
| Obito | A person of great depth |
| Oboe | A high pitched woodwind |
| Obsidian | A dark volcanic glass |
| Odinsh | A follower of the god Odin |
| Officer | One who holds a position of duty. |
| Ojasv | Possessing great inner strength. |
| Okemos | A name meaning little chief. |
| Okwari | A name meaning young bear. |
| Oluwaseun | God has done a great thing. |
| Onawi | A name meaning earth or soil. |
| Ondreaz | A variant of Andrew meaning manly. |
| Ong | A surname meaning king or royal. |
| Ooty | Named after the hill station town. |
| Optic | Relating to the sense of sight. |
| Orav | An Estonian name meaning squirrel. |
| Orbit | A curved path around a planet. |