| Ontario | Beautiful place, a Native American name meaning lovely location |
| Onyka | God is my joy, a Nigerian name meaning divine happiness |
| Oota dabun | Gift of the forest, a Native American name meaning woodland treasure |
| Optimus | Best, a Latin name meaning superior or excellent |
| Opus | Work, a Latin name meaning creation or achievement |
| Orev | God is my shepherd, a Hebrew name meaning divine guidance |
| Orie | God is my light, a Nigerian name meaning divine illumination |
| Orlagh | A golden princess or ruler. |
| Orley | Famous meadow, a French name meaning renowned pasture |
| Orlo | Famous hill, a Russian name meaning renowned elevation |
| Ormonda | Descendant of Ruadh |
| Ornat | Littlesallowone |
| Orrie | Famous warrior, a Gaelic name meaning renowned fighter |
| Ortona | Beautiful hill, an Italian name meaning lovely location |
| Ortwin | Spearhead, friend |
| Orvel | Derived from the golden city. |
| Orvon | Famous mountain, a Welsh name meaning renowned peak |
| Orwell | Derived from the surname of the English author George Orwell. |
| Oryon | Boundary, limit |
| Osanne | A prayer of praise to the Lord. |
| Osca | A champion of the divine spear. |
| Oscon | Possibly derived from the Latin word 'os,' meaning mouth. |
| Oslo | Derived from the Old Norse words 'óss' and 'ló,' meaning sacred meadow. |
| Osmel | Derived from the Latin word 'os,' meaning mouth, and the suffix '-mel.' |
| Otey | Derived from the Old English word 'ot,' meaning fire. |
| Othon | Wealth and prosperity |
| Otten | A name meaning wealthy or rich. |
| Otti | A name meaning wealthy and noble. |
| Oukouaka | Derived from the Greek words 'oukos' and 'ouka,' meaning good and noble. |
| Paol | Derived from the Latin name Paulus, meaning small. |
| Paoli | A name meaning small or humble. |
| Paoline | One who is small and little. |
| Parella | Derived from the Italian word 'parella,' meaning pair. |
| Parka | Derived from the Inuit word 'parka,' meaning parka coat. |
| Parks | Derived from the Old English word 'parc,' meaning enclosure. |
| Parkus | Derived from the Latin word 'parcus,' meaning frugal. |
| Patriccia | A noble man, patrician |
| Patriciaa | A noble man, patrician |
| Patrricia | A noble man, patrician |
| Pattricia | A noble man, patrician |