| Name | Origin | Meaning | Gender |
| O' | Irish | Descendent of. Irish surnames formed by prefacing O'. | male |
| O'brian | Irish | Surname. | male |
| O'brien | Irish | Surname. | male |
| O'keefe | Irish | Surname. | male |
| O'shay | Irish | Surname. | male |
| O'shea | Irish | Surname. | male |
| Oakden | English | From the oak tree valley | male |
| OAKES | english | from the oak | male |
| Oakes | English | From the oak | male |
| OAKLEY | english | from the oak-tree meadow | male |
| Oakley | English | From the oak - tree meadow | male |
| OBA | egyptian | king | male |
| Obadiah | Hebrew | Serves God | male |
| OBADIAH, | hebrew | serves God | male |
| OBASI | Africa | Ibo of Nigeria name meaning "in honor of the supreme God." | male |
| Obediah | Hebrew | Serves God | male |
| OBI | Africa | Ibo of Nigeria name meaning "heart." | male |
| OBIAREUS | greek | myth name (a Titan) | male |
| OBIKE | Africa | Ibo of Nigeria name meaning "a strong household." | male |
| OCEANUS | greek | myth name (father of the Oceanids) | male |
| OCELFA | english | from the high plain | male |
| Ocelfa | English | From the high plain | male |
| Ociel | Latin | Sky | male |
| OCNUS | greek | incompetent | male |
| OCTA | anglo | a son of Hengist | male |
| OCTAVE | french | born eighth | male |
| Octave | French | Born eighth | male |
| OCTAVIAN | romanian | eighth | male |
| Octe | Anglo-Saxon | A son of Hengist | male |
| OCTHA | arthurian | enemy of Arthur | male |
| Octha | Arthurian Legend | Enemy of Arthur | male |
| Octha | Anglo-Saxon | A son of Hengist | male |
| OCUMWHOWURST | native | Cheyenne name meaning " yellow wolf." | male |
| Ocumwhowurst | Native American | Yellow wolf (Cheyenne) | male |
| Ocunnowhurst | Native American | Yellow wolf (Cheyenne) | male |
| OCVRAN | arthurian | father of Guinevere | male |
| Ocvran | Arthurian Legend | Father of Guinevere | male |
| ODAKOTA | native | Sioux name meaning " friend." | male |
| Odakota | Native American | Friend (Sioux) | male |
| Odale | English | Of the valley | male |
| Odam | English | Son in law | male |
| Odanodan | Irish | Of the red earth | male |
| Odayle | English | Of the valley | male |
| Odbart | German | Wealthy | male |
| ODD | norse | point ODDLEIF | male |
| ODED | hebrew | encourages | male |
| Oded | Hebrew | Encourages | male |
| Odel | Anglo-Saxon | Wealthy | male |
| ODELL | anglo | wealthy | male |
| ODELL | english | of the valley | male |
| Odell | Irish | Surname. | male |
| Odell | English | Of the valley | male |
| Odell | Anglo-Saxon | Wealthy | male |
| ODERO | Africa | Luo of Kenya name meaning "granary." | male |
| ODHARNAIT | gaelic | pale | male |
| Odhert | German | Wealthy | male |
| Odhran | Irish | Pale green | male |
| Odi | Anglo-Saxon | Wealthy defender | male |
| Odin | Anglo-Saxon | Wealthy defender | male |
| ODION | Africa | Nigerian name meaning "first born of twins." | male |
| ODION | egyptian | born of twins | male |
| ODO | french | name of a bishop | male |
| Odo | French | Name of a bishop | male |
| ODOM | english | son-in-law | male |
| Odom | English | Son in law | male |
| ODON | anglo | wealthy defender | male |
| Odon | Anglo-Saxon | Wealthy defender | male |
| Odran | Irish | Pale green | male |
| Odwolf | English | Wealthy wolf | male |
| Odwolfe | English | Wealthy wolf | male |
| ODWULF | english | wealthy wolf | male |
| Odwulf | English | Wealthy wolf | male |
| Ody | Anglo-Saxon | Wealthy defender | male |
| ODYSSEUS | greek | wrathful | male |
| OEDIPUS | greek | swollen foot | male |
| Oegelsby | English | Fearsome | male |
| OENEUS | greek | myth name (king of Calydon) | male |
| Oengus | Irish | One vigor | male |
| OENOMAUS | greek | myth name (son of Ares) | male |
| OFER | hebrew | fawn | male |
| Ofer | Hebrew | Fawn | male |
| OFFA | anglo | name of a king | male |
| Offa | Anglo-Saxon | Name of a king | male |
| OGALEESHA | native | Sioux name meaning " wears a red shirt." | male |
| Ogaleesha | Native American | Wears a red shirt (Sioux) | male |
| OGDEN | english | from the oak-tree valley | male |
| Ogden | English | From the oak tree valley | male |
| Ogdon | English | From the oak tree valley | male |
| OGELSBY | english | fearsome | male |
| Ogelsby | English | Fearsome | male |
| Ogelsvie | English | Fearsome | male |
| Ogelsvy | English | Fearsome | male |
| OGIER | french | legend name | male |
| Ogilhinn | Scottish | From the high peak | male |
| Ogilvie | Scottish | From the high peak | male |
| OHANKO | native | reckless OHANZEE | male |
| Ohanko | Native American | Reckless | male |
| Ohanzee | Native American | Shadow (Sioux) | male |
| OHCUMGACHE | native | Cheyenne name meaning " little wolf." OHITEKAH | male |
| Ohcumgache | Native American | Little wolf (Cheyenne) | male |
| OHINI | Africa | Akan of Ghana name meaning "chief." | male |
| Ohitekah | Native American | Brave (Sioux) | male |
| OHTLI | nahuatl | unisexual name meaning "road." | male |
| Oidhche | Scottish | Night | male |
| OIGHRIG | greek | well-spoken | male |
| OJI | Africa | Ibo of Nigeria name meaning "bearer of gifts." | male |
| OJO | Africa | Yoruba of Nigeria name used when the birth was difficult. | male |
| OKE | hawaiian | a form of Oscar; divine strength | male |
| OKELLO | Africa | Ateso of Uganda name meaning "born after twins." | male |
| Okes | English | From the oak | male |
| Okhmhaka | Native American | Little wolf (Cheyenne) | male |
| OKO | Africa | Adangbe of Ghana name meaning "twin." | male |
| OKOTH | Africa | Ugandan name meaning "born during the rains." | male |
| OKPARA | egyptian | firstborn | male |
| OLA | Africa | Yoruba of Nigeria name meaning "wealth." | male |
| OLAF | danish | family | male |
| OLAMIDE | "Yoruba,Nigeria" | MY PROSPERITY HAS COME | male |
| OLES | greek | defender of man | male |
| Oliphant | Scottish | Great strength | male |
| Olis | German | "Powerful, strong." | male |
| OLIVER | french | legend name | male |
| Oliver | English | The olive tree. The biblical olive tree symbolizes fruitfulness and beauty and dignity. Extending an olive branch signifies an offer of peace. | male |
| Oliver | French | The olive tree. The biblical olive tree symbolizes fruitfulness and beauty and dignity. Extending an olive branch signifies an offer of peace. | male |
| Oliverio | Spanish | Affectionate | male |
| Oliverios | Spanish | Affectionate | male |
| OLIVIER | french | from the olive tree | male |
| Olivier | French | From the olive tree | male |
| Ollaneg | English | From Olney | male |
| OLLIN | nahuatl | movement | male |
| OLNEY | english | from Olney | male |
| Olney | English | From Olney | male |
| Oluwatosin | Yoruba | The Lord is worthy to be served | male |
| OMAR | arabic | first son; long life; most high; the prophet's follower | male |
| Omar | Hebrew | Speaker. 12th century Persian poet and astronomer and mathematician Omar Khayyam. Caliph Omar II made Islam an imperial power. | male |
| Omar | Arabic | Long-lived. | male |
| OMARI | egyptian | high born | male |
| Omari | Arabic | Full of life and prosperity. One who prospers and is full of life. | male |
| OMAWNAKW | native | Hopi name meaning " cloud feather." | male |
| Omawnakw | Native American | Cloud feather (Hopi) | male |
| Omeet | Hebrew | My light | male |
| Omer | Arabic | First son | male |
| Omet | Hebrew | My light | male |
| Ommar | Arabic | First son | male |
| OMRAN | arabic | solid structure | male |
| ONAN | turkish | prosperous | male |
| ONDRUS | czechoslovakian | manly | male |
| ONFROI | french | peaceful Hun | male |
| Onfroi | French | PeacefuI Hun | male |
| ONille | French | From the gold town | male |
| ONSLOW | english | from the zealous one's hill | male |
| Onslow | English | From the zealous one's hill | male |
| Onslowe | English | From the zealous one's hill | male |
| ONUR | turkish | honor | male |
| ONURIS | egyptian | brings back the distant one | male |
| Onyebuchi | Nigerian | Who is God? He is in everything | male |
| OPHELOS | greek | profit; help | male |
| OPHION | greek | myth name (a serpent) | male |
| OPHIR | hebrew | meaning unknown | male |
| Orahamm | English | From tbe riverbank enclosure | male |
| ORAM | english | from the riverbank enclosure | male |
| Oram | English | From tbe riverbank enclosure | male |
| Oran | Celtic | White | male |
| Oran | Irish | Pale green | male |
| Oratun | English | From the shore farm | male |
| Orbart | German | Wealthy | male |
| ORBERT | german | wealthy | male |
| Orbert | German | Wealthy | male |
| ORD | anglo | spear | male |
| Ord | Anglo-Saxon | Spear | male |
| Ordland | English | From the pointed hill | male |
| Ordman | English | Spearman | male |
| Ordmund | English | Spear defender | male |
| Ordsone | English | Ormond's son | male |
| Ordwald | English | Spear strength | male |
| ORDWAY | anglo | warrior armed with a spear | male |
| Ordway | Anglo-Saxon | Warrior armed with a spear | male |
| Ordwin | English | Spear friend | male |
| Ordwine | English | Spear friend | male |
| OREN | hebrew | tree | male |
| Oren | Hebrew | Pine tree. | male |
| ORESTES | greek | from the mountain | male |
| ORFORD | english | from the cattle ford | male |
| Orford | English | From the cattle ford | male |
| Orham | English | From tbe riverbank enclosure | male |
| ORI | hebrew | my light | male |
| Ori | Hebrew | My light | male |
| Orick | English | From the ancient oak tree | male |
| Orik | English | From the ancient oak tree | male |
| ORIN | celtic | white | male |
| Orin | Celtic | White | male |
| Orin | Hebrew | Tree | male |
| ORION | greek | son of fire | male |
| Orion | Greek | Son of Fire | male |
| Oris | Hebrew | Tree | male |
| ORLAN | english | from the pointed hill | male |
| Orlan | English | From the pointed hill | male |
| Orlan | German | Renowned in the land. Form of Roland. | male |
| Orlan | Spanish | Renowned in the land. Form of Roland. | male |
| Orland | German | Renowned in the land. Form of Roland. | male |
| Orland | English | From the pointed hill | male |
| Orland | Spanish | Renowned in the land. Form of Roland. | male |
| Orlando | German | Renowned in the land. Form of Roland. | male |
| Orlando | Spanish | Famous land | male |
| ORLEGE | anglo | battle strife | male |
| Orlege | Anglo-Saxon | Battle strife | male |
| Orlin | Spanish | Renowned in the land. Form of Roland. | male |
| Orlin | German | Renowned in the land. Form of Roland. | male |
| Orlondo | German | Renowned in the land. Form of Roland. | male |
| Orlondo | Spanish | Renowned in the land. Form of Roland. | male |
| ORMAN | english | spearman | male |
| Orman | English | Spearman | male |
| ORMEMAN | english | ship man | male |
| Ormeman | English | Spearman | male |
| ORMEMUND | english | spear-defender | male |
| Ormemund | English | Spear defender | male |
| ORMOD | anglo | sad | male |
| Ormod | Anglo-Saxon | Sad | male |
| Ormond | English | Spear defender | male |
| Ormund | English | Spear defender | male |
| Oro | Spanish | Gold | male |
| ORPHEUS | greek | myth name (son of Apollo) | male |
| Orran | English | The name of an English river. | male |
| Orren | English | The name of an English river. | male |
| ORRICK | english | from the ancient oak tree | male |
| Orrick | English | From the ancient oak tree | male |
| Orrik | English | From the ancient oak tree | male |
| Orrin | English | The name of an English river. | male |
| Orsen | English | Ormond's son | male |
| ORSON | english | Ormond's son | male |
| ORSON | french | little bear | male |
| Orson | English | Ormond's son | male |
| Orson | French | Little bear | male |
| ORTHROS | greek | myth name (guardian of Geryon) | male |
| ORTON | english | from the shore farm | male |
| Orton | English | From the shore farm | male |
| Ortun | English | From the shore farm | male |
| ORTZI | basque | meaning unknown | male |
| ORVAL | english | spear-strength | male |
| Orval | English | Spear strength | male |
| Orvelle | French | Gold town. | male |
| Orvil | English | Spear strength | male |
| Orvil | French | Gold town. | male |
| ORVILLE | french | from the gold town | male |
| Orville | French | Gold town. | male |
| Orville | English | Spear strength | male |
| ORVIN | anglo | brave friend | male |
| ORVIN | english | spear-friend | male |
| Orvin | Anglo-Saxon | Brave friend | male |
| Orvin | English | Spear friend | male |
| Orvyn | Anglo-Saxon | Brave friend | male |
| Orvyn | English | Spear friend | male |
| Orwald | English | Spear strength | male |
| Orwel | Welsh | Horizon | male |
| OS | english | divine | male |
| Os | English | Divine | male |
| OSAHAR | egyptian | God hears me | male |
| OSAZE | egyptian | loved by God | male |
| Osbart | English | Divinely brilliant | male |
| Osbeorht | English | Divinely brilliant | male |
| OSBERT | english | divinely brilliant | male |
| Osbert | English | Divinely brilliant | male |
| OSBORN | english | divine warrior | male |
| Osborn | English | Divine warrior | male |
| Osbourne | English | Divine warrior | male |
| Osburn | English | Divine warrior | male |
| Osburt | English | Divinely brilliant | male |
| OSCAR | celtic | jumping fighter | male |
| Oscar | English | God's spear. | male |
| Oscar | Celtic | Jumping fighter | male |
| Osckar | Celtic | Jumping fighter | male |
| OSIP | hebrew | God will multiply | male |
| Osip | Hebrew | God wiIl multiply | male |
| OSIRIS | egyptian | myth name (god of the dead) | male |
| Oskar | Celtic | Jumping fighter | male |
| OSKARI | finnish | leaping warrior | male |
| Osker | Celtic | Jumping fighter | male |
| OSLA | arthurian | meaning unknown | male |
| Osman | English | Godly protection. | male |
| OSMAR | english | divinely glorious | male |
| Osmar | English | Divinely glorious | male |
| Osmarr | English | Divinely glorious | male |
| Osmin | English | Godly protection. | male |
| OSMOND | english | divine protector | male |
| Osmond | English | Divine protector | male |
| Osmont | English | Divine protector | male |
| Osmund | English | Godly protection. | male |
| Osraed | English | Divine counselor | male |
| OSRED | english | divine counselor | male |
| Osred | English | Divine counselor | male |
| OSRIC | anglo | divine ruler | male |
| OSRIC | english | divine ruler | male |
| Osric | Anglo-Saxon | Divine ruler | male |
| Osric | English | Divine ruler | male |
| Osrick | English | Divine ruler | male |
| Osrid | English | Divine counselor | male |
| Osrik | English | Divine ruler | male |
| Osryd | English | Divine counselor | male |
| OSSIAN | celtic | meaning unknown | male |
| Ossian | Irish | Fawn | male |
| Osten | Latin | Worthy of Respect | male |