| Name | Meanings | Gender | Origin |
|---|---|---|---|
| Oakes | from the oak-tree grove | Boy | English |
| Oakley | Field of Oak Trees | Boy | Anglo-Saxon |
| Obelia | pillar of strength | Girl | Greek |
| Obert | Otter | Boy | German |
| Oceana | Ocean | Girl | Greek |
| Octavia | the eighth | Girl | Latin |
| Octavio | The Eighth | Boy | Latin |
| Odele | Wealthy | Girl | Greek |
| Odelia | I will praise god | Girl | Hebrew |
| Odera | plough | Girl | Hebrew |
| Odessa | a long journey | Girl | Greek |
| Odetta | Melody | Girl | |
| Odin | head god in Norse mythology | Boy | Scandinavian |
| Odon | wealthy protector | Boy | Hungarian |
| Odysseus | Full of Wrath | Boy | |
| Olaf | Ancestor (Dan) | Boy | Scandinavian |
| Olathe | beautiful | Girl | American Indian |
| Olga | Holy | Girl | Scandinavian |
| Oliana | oleander | Girl | Hawaiian |
| Olin | Holly | Boy | Scandinavian |
| Olinda | protector of property | Girl | German |
| Olive | Form of OLIVER. an olive | Girl | Latin |
| Oliver | an olive | Boy | Latin |
| Olivia | olive tree | Girl | Greek |
| Olwen | white track (legenday heroine) | Girl | Welsh |
| Olympia | Mountain of the Gods | Girl | Greek |
| Omar | life | Boy | Arabic |
| Ona | graceful one | Girl | Gaelic |
| Onida | the expected one | Girl | American Indian |
| Oona | One | Girl | |
| Opal | From the Opal Gemstone | Girl | Sanskrit |
| Ophelia | serpent | Girl | Greek |
| Ophira | Gold | Girl | |
| Oprah | Form of OPHIRA. Gold | Girl | Hebrew |
| Ora | Light | Girl | Latin |
| Oralie | golden | Girl | Latin |
| Oran | Green | Boy | Gaelic |
| Oren | ash-tree | Boy | Hebrew |
| Orenda | magic power | Girl | American Indian |
| Oria | From the Orient | Girl | Greek |
| Oriana | Golden One | Girl | Greek |
| Orianna | golden, dawning | Girl | Latin |
| Oriel | golden, angel of destiny | Girl | French |
| Oringo | He Who Likes the Hunt | Boy | African |
| Oriole | fair-haired | Girl | Latin |
| Orion | son of fire, the hunter | Boy | Greek |
| Orla | Golden Woman | Girl | Gaelic |
| Orlando | Land of Gold | Boy | German |
| Orlantha | from the land | Girl | German |
| Orman | spear man | Boy | English |