| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 641 | Omolf | Norse | Son of Armod. | M | |
| 642 | Onund | Norse | Son of Viking. | M | |
| 643 | OrIyg | Norse | Son of Valthjof. | M | |
| 644 | Orm | Norse | Son of Ulf. | M | |
| 645 | Os | Norse | Divine. | M | |
| 646 | Osborn | Norse | Divine bear. | M | |
| 647 | Osborne | Norse | Variant of Osborn: Divine bear. | M | |
| 648 | Oscar | Norse | Divine spear. | M | |
| 649 | Osgood | Norse | A divine Goth. | M | |
| 650 | Osk | Norse | Mother of Hild. | F | |
| 651 | Oskar | Norse | Divine spear. | M | |
| 652 | Ospak | Norse | Brother of Gudrun. | M | |
| 653 | Ostein | Norse | Happy. | M | |
| 654 | Osten | Norse | Happy. | M | |
| 655 | Osvif | Norse | Father of Gudrun. | M | |
| 656 | Othin | Norse | God of the sky. | M | |
| 657 | Ottar | Norse | Fighter. | M | |
| 658 | Ovaegir | Norse | Father of the Skraeling children. | M | |
| 659 | Ove | Norse | Ancestors. | M | |
| 660 | Oysten | Norse | Happy. | M | |