| Sikis | A name meaning to learn or study. |
| Sile | A name meaning a blind or sightless one. |
| Sine | A name meaning star or radiant. |
| Sineidin | A diminutive of God is gracious. |
| Siobhan | A name meaning God is gracious. |
| Siodhachan | Little peaceful one |
| Sive | A name meaning Lord Shiva. |
| Skylor | A name meaning a guardian of the sky. |
| Slaine | An Irish name meaning healthy or well. |
| Slany | A person hailing from the salt. |
| Sorcha | Bright, radiant, or luminous |
| Sorley | A summer sailor or traveler |
| Sosanna | A variant of the name Susanna. |
| Sruthair | From the stream |
| Sruthan | A person who is well learned. |
| Strahan | Derived from a Gaelic place name for a stream. |
| Struthers | From the stream |
| Suidhne | A name meaning little hero. |
| Suileabhan | One with dark, keen eyes. |
| SulliMn | A name meaning peaceful spirit. |
| Sullivan | Dark eyes. Surname. |
| Sun | From the town by the river Boyn |
| Suze | A diminutive form of Susan. |
| Sweeney | A small, heroic champion. |
| Sybil | One who is a divine oracle. |
| Taber | A name meaning a drummer boy. |
| Tadleigh | A name meaning meadow of toads. |
| Tag | Handsome. Variant of Teague. |
| Tagan | Tagan means 'strong' or 'powerful' in Mongolian, derived from the word 'tag', meaning 'strong' or 'firm'. |
| Taicligh | A name meaning dark hollow. |
| Taidhgin | "(pronounced Tee-gan), A poet or a philosopher." |
| Talfryn | from the top of the hill |
| Tally | A name meaning to count items. |
| Tangwyn | A name meaning fair or white fire. |
| Tara | From the crag of a tower.; Goddess of the sea.; A hill where the kings met; Where the kings met also Taras Halls were the place where ancient Bards sang deeds of Irish heroes. The ruins of the Halls are on the hill of Tara meaning crag or tower in Gaelic |
| Tarriannah | light of my life |
| Tate | Measure of land. |
| Tavion | Variant of the word teeve hillside. |
| Tavon | Variant of the word teeve hillside. |
| Tawnee | A green field; the warm sandy color of a lion's coat. |