| Name | Meaning | Gender | Origin |
|---|
| Oberon | noble, bearlike | Male | English |
| October | eighth | Female | Latin |
| Odessa | odyssey, journey, voyage | Female | Russian |
| Odette | happy home | Female | |
| Odile | prospers in battle | Female | |
| Odin | Viking mythology: the allmighty god | Male | Old |
| Olga | holy | Female | Russian |
| Olive | kind one; olive tree, peace. Symbol of peace. A small oval fruit. | Female | English |
| Oliver | The olive tree. The biblical olive tree symbolizes fruitfulness and beauty and dignity. Extending an olive branch signifies an offer of peace.
| Male | Latin |
| Olivia | Olive
| Female | Latin |
| Olympia | of Mount Olympus, heavenly | Female | Greek |
| Onyx | A gemstone with bands of different colours. | Male | |
| Opal | Australian gemstone of remarkable colours, usually red, blue or green | Female | Sanskrit |
| Opal | Australian gemstone of remarkable colours, usually red, blue or green | Female | Sanskrit |
| Ophelia | Serpentine
| Female | Greek |
| Orchid | | Female | |
| Orion | Son of Fire
| Male | Greek |
| Orla | Irish name meaning golden princess | Female | Irish |
| Orson | Little bear
| Male | Latin |
| Osborn | Soldier of God | Male | English |
| Osiris | with strong eyesight | Male | Egyptian |
| Oswald | Divinely powerful
| Male | English |
| Otis | Wealthy.
| Male | |
| Owen | Young fighter
| Male | Welsh |
| Paco | Eagle
| Male | Spanish |