| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 401 | Nisien | Celtic | Mythical son of Euroswydd. | M | |
| 402 | Nolan | Celtic | Noble. | M | |
| 403 | Noland | Celtic | Noble. | M | |
| 404 | Nyle | Celtic | Champion. | M | |
| 405 | Oran | Celtic | White. | M | |
| 406 | Orin | Celtic | White. | M | |
| 407 | Oscar | Celtic | Jumping fighter. | M | |
| 408 | Osckar | Celtic | Jumping fighter. | M | |
| 409 | Oskar | Celtic | Jumping fighter. | M | |
| 410 | Osker | Celtic | Jumping fighter. | M | |
| 411 | Owen | Celtic | Young fighter. | M | |
| 412 | Owin | Celtic | Young fighter. | M | |
| 413 | Owyn | Celtic | Young fighter. | M | |
| 414 | Pert | Celtic | From the thorn bush or thicket. | M | |
| 415 | Perth | Celtic | From the thorn bush or thicket. | M | |
| 416 | Phelan | Celtic | Wolf. | M | |
| 417 | Piran | Celtic | St. Piran is the Cornish patron saint of miners. | M | |
| 418 | Powell | Celtic | Son of Howell. | M | |
| 419 | Pryderi | Celtic | Care. | M | |
| 420 | Pwyll | Celtic | Mythical lord of Annwn. | M | |