| Name | Group | Language of Origin | Languages of Use | Meaning/Translation or Related Words | US 2021 |
| Oakley | Oakley | Old English | English | oak field | #403 |
| Ocean | Ocean | English | English | ocean | #711 |
| Octave | Octavius/Octavia | Latin | French | the eighth, born in the eighth month | |
| Octavian | Octavius/Octavia | Latin | German, English | the eighth, born in the eighth month | |
| Octavio | Octavius/Octavia | Latin | Spanish | the eighth, born in the eighth month | |
| Octavius | Octavius/Octavia | Latin | German, English | the eighth, born in the eighth month | |
| Odd | Odd | Old Norse | Scandinavian | point of a weapon | |
| Oddone | Oddone | Old High German | Italian | | |
| Odhrán | Odhrán | Old Irish | Irish | little pale green one | |
| Odin | Odin | Old Norse | Scandinavian | the inspired | #327 |
| Óðinn | Odin | Old Norse | Icelandic | the inspired | |
| Odo | Otto/Ute | Old High German | German, Italian | Words: wealth | |
| Odoaker | Ottokar | Old High German | German | Words: wealth / vigilant | |
| Ofentse | Ofentse | Unknown | Zulu | | |
| Ognjen | Ognyan | Bulgarian | Serbo-Croatian | fiery | |
| Ognyan | Ognyan | Bulgarian | Bulgarian | fiery | |
| Ohad | Ehud | Hebrew | Hebrew | united | |
| Oisín | Oisín | Old Irish | Irish | | |
| Oiva | Oiva | Finnish | Finnish | splendid, excellent | |
| Okke | Okke | Frisian | Frisian | Words: wealth | |
| Okko | Okke | Frisian | Frisian | Words: wealth | |
| Oktavian | Octavius/Octavia | Latin | German | the eighth, born in the eighth month | |
| Oktavus | Octavius/Octavia | Latin | German | the eighth, born in the eighth month | |
| Oktay | Oktay | Unknown | Turkish | | |
| Ola | Olaf/Olava | Old Norse | Scandinavian | ancestor's descendant | |
| Olaf | Olaf/Olava | Old Norse | German, English, Scandinavian | ancestor's descendant | |
| Ólafur | Olaf/Olava | Old Norse | Icelandic | ancestor's descendant | |
| Olai | Olaf/Olava | Old Norse | Scandinavian | ancestor's descendant | |
| Olav | Olaf/Olava | Old Norse | Scandinavian | ancestor's descendant | |
| Olavi | Olaf/Olava | Old Norse | Finnish | ancestor's descendant | |
| Ole | Olaf/Olava | Old Norse | German, Low German, Scandinavian | ancestor's descendant | |
| Oleg | Helge/Helga | Old Norse | Russian | holy, blessed | |
| Olek | Alexander/Alexandra | Old Greek | Polish | he who wards off (other) men, defender of men | |
| Oli | Oliver | Old High German | English | Words: elf / army, warrior / olive, olive tree | |
| Olindo | Olinto | Old Greek | Italian | | |
| Olinto | Olinto | Old Greek | Italian | | |
| Oliver | Oliver | Old High German | German, English | Words: elf / army, warrior / olive, olive tree | #3 |
| Olivér | Oliver | Old High German | Hungarian | Words: elf / army, warrior / olive, olive tree | |
| Óliver | Oliver | Old High German | Icelandic | Words: elf / army, warrior / olive, olive tree | |
| Ólíver | Oliver | Old High German | Icelandic | Words: elf / army, warrior / olive, olive tree | |
| Olivers | Oliver | Old High German | Latvian | Words: elf / army, warrior / olive, olive tree | |
| Olivier | Oliver | Old High German | French | Words: elf / army, warrior / olive, olive tree | |
| Oliviero | Oliver | Old High German | Italian | Words: elf / army, warrior / olive, olive tree | |
| Oliwier | Oliver | Old High German | Polish | Words: elf / army, warrior / olive, olive tree | |
| Olle | Olaf/Olava | Old Norse | Scandinavian | ancestor's descendant | |
| Ollie | Oliver | Old High German | English | Words: elf / army, warrior / olive, olive tree | |
| Olly | Oliver | Old High German | English | Words: elf / army, warrior / olive, olive tree | |
| Olof | Olaf/Olava | Old Norse | Scandinavian | ancestor's descendant | |
| Olov | Olaf/Olava | Old Norse | Scandinavian | ancestor's descendant | |
| Olve | Olve | Unknown | Scandinavian | | |
| Omar | Umar | Arabic | Malay, Arabic | flourishing, long-living | #264 |
| Omari | Umar | Arabic | English | flourishing, long-living | #492 |
| Omarion | Omarion | Unknown | English | | |
| Omer | Omer | Unknown | German | | |
| Ömer | Umar | Arabic | Turkish | flourishing, long-living | |
| Ömer Asaf | Ömer Asaf | Unknown | Turkish | | |
| Ömer Faruk | Ömer Faruk | Turkish | Turkish | | |
| Ömer Halis | Ömer Halis | Turkish | Turkish | | |
| Omero | Homer | Old Greek | Italian | | |
| Omphile | Omphile | Sesotho | Sesotho | maybe given | |
| Ömür | Ömür | Turkish | Turkish | life span | |
| Ondrej | Andrew/Andrea | Old Greek | Czech | the manly, the brave | |
| One | One | Unknown | Frisian | | |
| Onni | Onni | Finnish | Finnish | luck | |
| Onno | One | Unknown | Frisian | | |
| Onofrio | Onofrio | Old Greek | Italian | | |
| Onorato | Honoré/Honorée | Latin | Italian | Words: honor | |
| Onur | Onur | Turkish | Turkish | honor | |
| Onyx | Onyx | Unknown | English | | #406 |
| Oran | Odhrán | Old Irish | Irish | little pale green one | |
| Orazio | Horaz | Etrusk | Italian | | |
| Orçun | Orçun | Unknown | Turkish | | |
| Orell | Aurel/Aurelia | Latin | German, Swiss German | Words: golden | |
| Orest | Oreste/Orestina | Old Greek | Slavic | | |
| Oreste | Oreste/Orestina | Old Greek | Italian | | |
| Orfeo | Orfeo | Old Greek | Italian | Words: darkness | |
| Orhan | Orhan | Turkish | Turkish | | |
| Orio | Orio | Unknown | Italian | | |
| Oriol | Oriol | Latin | Catalan | Words: golden | |
| Orion | Orion | Old Greek | German, English | Words: urine | #314 |
| Orlando | Roland/Rolanda | Old High German | Spanish, Italian | Words: fame / land, homeland | #753 |
| Oronzio | Oronzo | Unknown | Italian | | |
| Oronzo | Oronzo | Unknown | Italian | | |
| Orsino | Ursino | Latin | Italian | Words: bear | |
| Orso | Urs | Latin | Italian | the bear | |
| Orson | Orson | Old French | English | | |
| Ortensio | Ortensio/Hortensia | Latin | Italian | | |
| Ortwin | Ortwin | Old High German | German | Words: friend | |
| Osama | Usama | Arabic | Arabic | the lion | |
| Osamu | Osamu | Japanese | Kanji symbol, Japanese | Words: study, repair, cultivate | |
| Osbaldo | Oswald | Old High German | English | Words: Ass / rule | |
| Osbert | Osbert | Old English | German, English | Words: deity / bright | |
| Oscar | Oskar | Old Norse | Italian, English, French | Words: ase, deity / spear | #226 |
| Óscar | Oskar | Old Norse | Spanish | Words: ase, deity / spear | |
| Osiris | Osiris | Egyptian | English | | #947 |
| Oskar | Oskar | Old Norse | German | Words: ase, deity / spear | |
| Óskar | Oskar | Old Norse | Icelandic | Words: ase, deity / spear | |
| Oskari | Oskar | Old Norse | Finnish | Words: ase, deity / spear | |
| Osman | Osman | Arabic | Malay, Turkish | bustard fledgling | #981 |
| Ossian | Oisín | Old Irish | English | | |