| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 641 | Penarddun | Celtic | Mythical daughter of Beli. | F | |
| 642 | Pert | Celtic | From the thorn bush or thicket. | M | |
| 643 | Perth | Celtic | From the thorn bush or thicket. | M | |
| 644 | Phelan | Celtic | Wolf. | M | |
| 645 | Piran | Celtic | St. Piran is the Cornish patron saint of miners. | M | |
| 646 | Powell | Celtic | Son of Howell. | M | |
| 647 | Pryderi | Celtic | Care. | M | |
| 648 | Pwyll | Celtic | Mythical lord of Annwn. | M | |
| 649 | Quin | Celtic | Wise. | M | |
| 650 | Quinn | Celtic | Wise. | M | |
| 651 | Reagan | Celtic | Regal. | M | |
| 652 | Reaghan | Celtic | Nobility. | F | |
| 653 | Reaghan | Celtic | Regal. | M | |
| 654 | Regan | Celtic | Nobility. | F | |
| 655 | Regan | Celtic | Regal. | M | |
| 656 | Reghan | Celtic | Regal. | M | |
| 657 | Rhiannon | Celtic | Mythical daughter of Hefeydd. | F | |
| 658 | Ronan | Celtic | Oath. | M | |
| 659 | Ronat | Celtic | Seal. | F | |
| 660 | Rowena | Celtic | White or comely. | F | |