| Name | Meaning |
| Oakes | Oak Trees |
| Oakley | Oak-tree Field |
| Obed | A Short Form of Obadiah |
| Ogden | Oak Valley. |
| Olin | Holly |
| Ollie | A Familiar Form of Oliver |
| Onslow | Enthusiast's Hill |
| Ormond | Bear Mountain; Spear Protector |
| Orrick | Old Oak Tree |
| Orrin | River |
| Orton | Shore Town |
| Orval | A Form of Orville |
| Orvin | Spear Friend |
| Osbert | Divine; Bright |
| Osborn | Warrior of God |
| Osgood | Divinely Good |
| Osmar | Divine; Wonderful |
| Osmond | Divine Protector. |
| Osric | Divine Ruler |
| Oswald | God's Power; God's Crest |
| Oswin | Divine Friend. |
| Overton | High Town |
| Oxford | Place Where Oxen Cross The River |
| Oxley | Ox Meadow |
| Oxton | Ox Town |
| Ozzie | A Familiar Form of Osborn |
| Ozzy | A Familiar Form of Osborn |
| Christian Baby Boy Names Starting with Letter |
| A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |