| Sienna | | see-EN-ə | English (Modern) | |
| Sierra | | see-ER-ə | English (Modern) | |
| Sigmund | | ZEEK-muwnt (German), SIG-mənd (English) | German, Swedish, Norwegian, Danish, English | |
| Silas | | SIE-ləs (English) | English, Greek, Biblical, Biblical Latin, Biblical Greek | |
| Silver | | SIL-vər | English | |
| Silvester | | sil-VES-tər (English) | Dutch, English, Slovene, Slovak, German, Late Roman | |
| Silvia | | SEEL-vyah (Italian), SEEL-byah (Spanish) | Italian, Spanish, Portuguese, Romanian, Slovak, English, German, Late Roman, Roman Mythology | |
| Simon | | SIE-mən (English), see-MAWN (French), ZEE-mawn (German), SEE-mawn (Dutch) | English, French, Swedish, Norwegian, Danish, German, Dutch, Hungarian, Slovene, Romanian, Macedonian | |
| Simone (1) | | see-MON (French) | French, English | |
| Simonette | | - | English (Rare) | |
| Sinclair | | sin-KLER | English (Rare) | |
| Sindy | | SIN-dee | English (Rare) | |
| Sinjin | | - | English (Rare) | |
| Sissie | | SIS-ee | English | |
| Sissy | | SIS-ee | English | |