| # | Name | Origin | Meaning | Gender | |
|---|---|---|---|---|---|
| 821 | Sayers | Welsh | Carpenter. | M | |
| 822 | Sayre | Welsh | Carpenter. | M | |
| 823 | Sayres | Welsh | Carpenter. | M | |
| 824 | Seith | Welsh | Seven. | M | |
| 825 | Sel | Welsh | Legendary son of Selgi. | M | |
| 826 | Selwyn | Welsh | Ardour; fair. | M | |
| 827 | Selyf | Welsh | Welsh form of Solomon 'peace'. | M | |
| 828 | Selyv | Welsh | Legendary son of Kynan. | M | |
| 829 | Seren | Welsh | Star. | F | |
| 830 | Sian | Welsh | Welsh form of Jane: God is gracious. God's gift. | F | |
| 831 | Siarl | Welsh | Welsh form of Charles 'manly'. | M | |
| 832 | Siawn | Welsh | Legendary son of Iaen. | M | |
| 833 | Siencyn | Welsh | Welsh form of Jenkin 'God is gracious'. | M | |
| 834 | Sinnoch | Welsh | Legendary son of Seithved. | M | |
| 835 | Sion | Welsh | Welsh form of John 'God is gracious'. | M | |
| 836 | Sioned | Welsh | Welsh form of Jane: God is gracious. God's gift. | F | |
| 837 | Sior | Welsh | Welsh form of George 'farmer'. | M | |
| 838 | Steffan | Welsh | Crown; wreath. Variant of Stephen. | M | |
| 839 | Steffen | Welsh | Crown; wreath. Variant of Stephen. | M | |
| 840 | Steffon | Welsh | Crown; wreath. Variant of Stephen. | M | |