| Name | Meaning | Gender | Origin |
|---|
| Ocean | | Male | |
| Octavius | eighth | Male | Latin |
| Odie | Melody | Unisex | French |
| Odysseus | full of wrath | Male | Greek |
| 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 |
| Omen | | Male | |
| Ondine | little wave | Female | Latin |
| 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 |
| Orange | Round citrus fruit originating in Southeast Asia. | Female | Fruit |
| Orange | Round citrus fruit originating in Southeast Asia. | Female | Fruit |
| Oreo | American cookie brand consisting of two chocolate wafers with white cream filling. | Male | |
| Oreo | American cookie brand consisting of two chocolate wafers with white cream filling. | Male | |
| Orion | Son of Fire
| Male | Greek |
| Orla | Irish name meaning golden princess | Female | Irish |
| Orville | Gold town.
| Male | |
| Oscar | God's spear.
| Male | English |
| Othello | he has the sound of God | Male | Hebrew |
| Othelo | | Unisex | |
| Otis | Wealthy.
| Male | |
| Otto | Born eighth or wealthy
| Male | |
| Oz | strength | Male | Hebrew |