| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 621 | Odell | Norse | Wealthy. | M | |
| 622 | Odin | Norse | God of the sky. | M | |
| 623 | Oilibhear | Norse | Relic. | M | |
| 624 | Ola | Norse | Descendant. | F | |
| 625 | Ola | Norse | Relic. | M | |
| 626 | Olaf | Norse | Relic; ancestral heritage. St. Olaf is the patron saint of Norway, and there were many kings in Scandinavia named Olaf. | M | |
| 627 | Olaug | Norse | Of the ancestors. | F | |
| 628 | Olav | Norse | Variant of Olaf: Relic; ancestral heritage. | M | |
| 629 | Olave | Norse | Variant of Olaf: Relic; ancestral heritage. | M | |
| 630 | Ole | Norse | Relic. | M | |
| 631 | Oleif | Norse | Relic descendant. | M | |
| 632 | Olen | Norse | Relic. | M | |
| 633 | Olga | Norse | Holy. | F | |
| 634 | Olin | Norse | Relic. | M | |
| 635 | Oliver | Norse | Affectionate. | M | |
| 636 | Olof | Norse | Relic. | M | |
| 637 | Olvaerr | Norse | Affectionate. | M | |
| 638 | Olvir | Norse | Affectionate. | M | |
| 639 | Olyn | Norse | Relic. | M | |
| 640 | Om | Norse | Father of Idunn. | M | |