| Name | Meaning | Gender | Origin |
|---|
| Ivan | Form of John | Male | Russian |
| Ivar | yew wood, archer | Male | Norse |
| Ivor | yew | Male | Scottish |
| Ivy | ivy plant, a wine | Female | Plant |
| Oakley | from the oak meadow | Male | English |
| Oberon | noble, bearlike | Male | English |
| Octavia | eighth | Female | Latin |
| Odessa | odyssey, journey, voyage | Female | Russian |
| Odin | Viking mythology: the allmighty god | Male | Old |
| 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 |
| Omar | first son, disciple; gifted speaker; famous | Male | Arabic |
| Oona | lamb | Female | Irish |
| Orchid | | Female | |
| Orion | Son of Fire
| Male | Greek |
| Orla | Irish name meaning golden princess | Female | Irish |
| Orson | Little bear
| Male | Latin |
| Oscar | God's spear.
| Male | English |
| Otis | Wealthy.
| Male | |
| Otto | Born eighth or wealthy
| Male | |
| Owen | Young fighter
| Male | Welsh |
| Oxford | From the ox ford
| Male | English |
| Ula | Abbreviation of Eulalie
| Female | Celtic |