| Name | Meaning | Gender | Origin |
|---|
| Odysseus | full of wrath | Male | Greek |
| 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 |
| Ollie | Latin, olive tree | Male | English |
| Olly | | Unisex | |
| OMalley | | Male | Hebrew |
| 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 |
| Orange | Round citrus fruit originating in Southeast Asia. | Female | Fruit |
| Orange | Round citrus fruit originating in Southeast Asia. | Female | Fruit |
| Orchid | | Female | |
| 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 |
| Orpheus | | Male | |
| Oscar | God's spear.
| Male | English |
| Osiris | with strong eyesight | Male | Egyptian |
| Othello | he has the sound of God | Male | Hebrew |
| Otto | Born eighth or wealthy
| Male | |
| Ozzie | Strong
| Male | Short |
| Pallas | wisdom | Female | Greek |
| Pan | all or shepherd | Male | Greek |
| Panda | A bear like Chinese mammal, with distinct black and white markings | Male | |