| Name | Meaning | Gender | Origin |
|---|
| Olivia | Olive
| Female | Latin |
| Ollie Bollie Mc Follie | | Unisex | Hebrew |
| Omaha | | Unisex | Hebrew |
| OMalley | | Male | Hebrew |
| Omega | great | Male | Greek |
| Onion | | Unisex | 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 |
| Ophelia | Serpentine
| Female | Greek |
| Opie | | Unisex | |
| Oprah | Fawn | Female | Hebrew |
| Orange Harvey | | Unisex | Hebrew |
| Orbit | | Male | Hebrew |
| Orca | | Unisex | |
| 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 |
| Orlando | Famous land
| Male | Italian |
| Orpheus | | Male | |
| Oscar | God's spear.
| Male | English |
| Osiris | with strong eyesight | Male | Egyptian |
| Oso | Bear. Oso for males and Osa for females. | Unisex | |
| Oster | | Unisex | |