| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 541 | Oilbhe | Irish | Olive. | F | |
| 542 | Olive | Irish | Olive. | F | |
| 543 | Oma | Irish | The color of olive. | F | |
| 544 | Omat | Irish | The color of olive. | F | |
| 545 | Ona | Irish | One. Also a variant of Una: Lamb; together. | F | |
| 546 | Onora | Irish | Honor. | F | |
| 547 | Oona | Irish | Variant of Oonagh: Lamb. Can also be an Irish variant of Latin Una: One. | F | |
| 548 | Oonagh | Irish | Lamb. Can also be an Irish variant of Latin Una': One. | F | |
| 549 | Orghlaith | Irish | Golden. | F | |
| 550 | Orla | Irish | Golden. | F | |
| 551 | Orlaith | Irish | Golden. | F | |
| 552 | Orlaithe | Irish | Golden. | F | |
| 553 | Padraigin | Irish | Noble. | F | |
| 554 | Phiala | Irish | Saintname. | F | |
| 555 | Raicheal | Irish | Name of a saint. | F | |
| 556 | Ranait | Irish | Wealthy or charming. | F | |
| 557 | Ranalt | Irish | Wealthy or charming. | F | |
| 558 | Rathnait | Irish | Wealthy or charming. | F | |
| 559 | Renny | Irish | Wealthy or charming. | F | |
| 560 | Richael | Irish | Name of a saint. | F | |