| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 621 | Nisien | Celtic | Mythical son of Euroswydd. | M | |
| 622 | Nola | Celtic | Famous. | F | |
| 623 | Nolan | Celtic | Noble. | M | |
| 624 | Noland | Celtic | Noble. | M | |
| 625 | Nyle | Celtic | Champion. | M | |
| 626 | Oifa | Celtic | Mythical sister of Ove. | F | |
| 627 | Oilell | Celtic | A mythical queen. | F | |
| 628 | Olwen | Celtic | Mythical daughter of Yspaddaden. | F | |
| 629 | Olwyn | Celtic | Mythical daughter of Yspaddaden. | F | |
| 630 | Oran | Celtic | White. | M | |
| 631 | Oriana | Celtic | Blond. | F | |
| 632 | Orin | Celtic | White. | M | |
| 633 | Oscar | Celtic | Jumping fighter. | M | |
| 634 | Osckar | Celtic | Jumping fighter. | M | |
| 635 | Oskar | Celtic | Jumping fighter. | M | |
| 636 | Osker | Celtic | Jumping fighter. | M | |
| 637 | Ove | Celtic | Mythical daughter of Dearg. | F | |
| 638 | Owen | Celtic | Young fighter. | M | |
| 639 | Owin | Celtic | Young fighter. | M | |
| 640 | Owyn | Celtic | Young fighter. | M | |