| Sinatra | Man | Italian Names |
| Sincere | Man | American Names |
| Sincerely | Woman | English Names |
| Sincerity | Woman | American Names |
| Sinclair | Man | English Names |
| Sine | Woman | Scottish Names |
| Sinead | Woman | Irish Names |
| Sinforoso | Man | Spanish Names |
| Singh | Unisex | Indian Names |
| Singleton | Unisex | English Names |
| Sinjin | Man | English Names |
| Siobhan | Woman | Irish Names |
| Síofra | Woman | Irish Names |
| Sion | Man | Hebrew Names |
| Sioned | Woman | Welsh Names |
| Sionn | Man | Irish Names |
| Sioux | Unisex | Native American Names |
| Sipeta | Woman | Native American - Miwok Names |
| Sir | Man | English Names |
| Siraj | Man | Arabic Names |