| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 581 | Sadwm | Welsh | Welsh form of Saturn 'god of the harvest'. | M | |
| 582 | Saer | Welsh | Carpenter. | M | |
| 583 | Saith | Welsh | Seven. | M | |
| 584 | Sayer | Welsh | Carpenter. | M | |
| 585 | Sayers | Welsh | Carpenter. | M | |
| 586 | Sayre | Welsh | Carpenter. | M | |
| 587 | Sayres | Welsh | Carpenter. | M | |
| 588 | Seith | Welsh | Seven. | M | |
| 589 | Sel | Welsh | Legendary son of Selgi. | M | |
| 590 | Selwyn | Welsh | Ardour; fair. | M | |
| 591 | Selyf | Welsh | Welsh form of Solomon 'peace'. | M | |
| 592 | Selyv | Welsh | Legendary son of Kynan. | M | |
| 593 | Siarl | Welsh | Welsh form of Charles 'manly'. | M | |
| 594 | Siawn | Welsh | Legendary son of Iaen. | M | |
| 595 | Siencyn | Welsh | Welsh form of Jenkin 'God is gracious'. | M | |
| 596 | Sinnoch | Welsh | Legendary son of Seithved. | M | |
| 597 | Sion | Welsh | Welsh form of John 'God is gracious'. | M | |
| 598 | Sior | Welsh | Welsh form of George 'farmer'. | M | |
| 599 | Steffan | Welsh | Crown; wreath. Variant of Stephen. | M | |
| 600 | Steffen | Welsh | Crown; wreath. Variant of Stephen. | M | |