| Name | Meaning | Origin | Gender |
| OAKES | Beside the Oak Trees | English | E |
| OAKLEY | Field of Oak Trees | English | E |
| OBEDIENCE | To Obey | American | E |
| OBELIA | Needle | Greek | F |
| OBERON | Bear Heart | German | E |
| OBERT | Wealthy | German | E |
| OCEAN | Sea | Greek | F |
| OCEANA | From the Sea | Greek | F |
| OCTAVIA | The Eighth | Latin | F |
| OCTAVIO | The Eighth | Latin | M |
| OCTAVIOUS | Eighth | Latin | M |
| OCTAVIUS | The Eighth | Greek | M |
| ODED | Strong | Hebrew | M |
| ODEDA | Strong | Hebrew | F |
| ODELE | Wealthy, Melody | Greek | F |
| ODELIA | I will praise God | Greek | F |
| ODELL | Otter | English | E |
| ODESSA | The Odyssey | Latin | F |
| ODETTA | Ode | French | F |
| ODETTE | Ode, Melodic | French | F |
| ODIN | Supreme God | Scandinavian | E |
| ODINA | Mountain | Latin | F |
| ODYSSEUS | Full of Wrath | Greek | M |
| OFIRA | Gold | Hebrew | F |
| OGDEN | From the Valley of Oaks | English | M |
| OIHANE | From the Forest | Spanish | F |
| OISTIN | Venerable | Latin | E |
| OJAL | Vision | Hindi | F |
| OKAL | To Cross | African | E |
| OKALANI | Heaven | Hawaiian | F |
| OKAPI | Animal with Long Neck | African | E |
| OKE | Form of OSCAR | Hawaiian | E |
| OKI | Ocean Centered | Japanese | F |
| OKOTH | Born when it was Raining | African | E |
| OKSANA | God is With Us | Slavic | F |
| OLAF | Ancestor | Scandinavian | M |
| OLEG | Sacred | Slavic | M |
| OLENCIA | Not available | American | F |
| OLESIA | Protector of Humanity | Polish | F |
| OLGA | Holy | Slavic | F |
| OLIANA | From Oleander | Hawaiian | F |
| OLIN | Of the Ancestors | Scandinavian | E |
| OLINA | Joyous | Hawaiian | F |
| OLINDA | Form of YOLANDA | Latin | F |
| OLIVE | Olive Branch, Peace | Latin | F |
| OLIVER | Olive Tree- Peace | Latin | M |
| OLIVIA | Peace - of the olive tree | Latin | F |
| OLLIE | From the name OLIVER | Greek | M |
| OLWEN | White footprint | Welsh | F |
| OLYMPE | Olympian | French | F |
| OLYMPIA | Mountain of the Gods | Greek | F |
| OMA | Commander | Arabic | M |
| OMANA | A Woman | Hindi | F |
| OMAR | Ultimate Devotee | Arabic | M |
| OMEGA | Last | Greek | E |
| ON | Peace | Chinese | M |
| ONA | Full of Grace | Latin | F |
| ONAEDO | Gold | African | F |
| ONAN | Wealthy | Turkish | M |
| ONAONA | Sweet Smell | Hawaiian | F |
| ONDREA | Strong, Courageous | Slavic | F |
| ONELLA | Torch Light | Hungarian | F |
| ONOFRE | Defender of Peace | Spanish | M |
| ONSLOW | Hill of the Passionate One | Arabic | M |
| ONTIBILE | God is Watching Over Me | African | F |
| OONA | One | Celtic/Gaelic | F |
| OPAL | Precious gem | Hindi | F |
| OPHELIA | Helper | Greek | F |
| OPHIRA | Gold | Greek | F |
| OPHRAH | Light | Hebrew | F |
| OPRAH | Runaway | Hebrew | F |
| ORA | Gold | Spanish | F |
| ORAL | Speaker, Word | Latin | M |
| ORALEE | Lord Is My Light | Hebrew | F |
| ORAN | Green | Celtic/Gaelic | E |
| ORANE | Rising | Greek | E |
| ORDE | Beginning | Latin | E |
| ORDELL | Beginning | Latin | E |
| OREA | Mountains | Greek | F |
| OREN | A Tree | Hebrew | M |
| ORESTES | Mountain Man | Greek | M |
| ORIA | From the Orient | Latin | F |
| ORIANA | Golden Dawn | Latin | F |
| ORIEL | Gold | French | E |
| ORIEN | The Orient, East | Latin | E |
| ORINDA | Pine Trees | Hebrew | F |
| ORINGO | He Who Likes the Hunt | African | M |
| ORIOLE | Golden; a gold flecked bird | Latin | E |
| ORION | A Hunter in Greek Mythology | Greek | E |
| ORLANDO | Land of Gold | Spanish | M |
| ORLEANS | Golden | French | E |
| ORLI | The Light is Mine | Hebrew | F |
| ORLY | Light | Hebrew | E |
| ORMA | Free Men | African | F |
| ORMAND | Serpent | German | M |
| ORMANDA | Of the Sea | German | F |
| ORNICE | Cedar Tree | Hebrew | M |
| ORO | Gold | Spanish | M |
| ORPAH | Fawn | Hebrew | F |
| ORRICK | Venerable Oak | English | M |
| ORRIN | River | English | M |
| ORSEN | From the name ORSON | Latin | M |
| ORSIN | Bear | Latin | M |
| ORSON | A Bear | Latin | M |
| ORVILLE | Golden City | French | M |
| OSAMA | Lion-Like | Arabic | M |
| OSANNA | Praise! | Greek | F |
| OSBORN | Bear of God | Scandinavian | M |
| OSBOURNE | Born from a Bear | Scandinavian | M |
| OSCAR | Accurate spearsman | Scandinavian | M |
| OSGOOD | Goth of the Heavens | English | M |
| OSIAS | Salvation | Greek | M |
| OSMA | God's Servant | Latin | F |
| OSMAN | Tender Youth | Arabic | M |
| OSMOND | Godly Protector | English | M |
| OSRIC | Divine Ruler | English | M |
| OSSIE | God's Divine Power | English | M |
| OSWALD | God of the Forest | English | M |
| OTHELLO | Prosperous | Greek | M |
| OTIENO | Born at Night | African | M |
| OTIS | One Who Hears Well | Greek | M |
| OTTO | Wealthy | German | M |
| OTYLIA | Lucky Heroine | German | F |
| OUIDA | Warrior Woman | French | F |
| OVA | Egg | Latin | F |
| OVERTON | The Upper Town | English | E |
| OVID | Egg Shaped | Latin | M |
| OVIDIO | Shepherd | Spanish | M |
| OWEN | Born to nobility | Celtic/Gaelic | M |
| OWENA | Well-born | Welsh | F |
| OWNAH | Form of UNA | Celtic/Gaelic | F |
| OZ | Strength | Hebrew | E |
| OZZIE | God's Divine Power | English | M |
| OZZY | God's Divine Power | English | M |