| Sky | Sky | Unisex | Norse |
| Skye | Cloud | Male | Norse |
| Skyler | Guarded | Unisex | Dutch |
| Slade | Valley | Male | English |
| Slash | | Unisex | Hebrew |
| Slinky | | Unisex | Hebrew |
| Sloane | Fighter | Unisex | American English |
| Smith | A smith | Male | English |
| Smokey | A grayish blue colour. Slang for highway patrol officer | Unisex | English |
| Smores | | Unisex | Hebrew |
| Smudge | A blotch or smear | Unisex | English |
| Snickers | A brand of candy bar. | Unisex | English |
| Snowball | | Unisex | Hebrew |
| Snowcone | | Unisex | Hebrew |
| Snuggles | To curl up closely, cuddle | Unisex | English |
| Socks | Short stockings finishing above the ankle | Unisex | English |
| Socrates | Uncertain meaning | Male | Greek |
| Solo | | Unisex | Hebrew |
| Sonny | Son | Male | English |
| Sooty | Covered with soot | Unisex | English |
| Spam | | Unisex | Hebrew |
| Spanky | | Unisex | Hebrew |
| Sparkle | To shine with animation | Unisex | English |
| Sparky | Animated, lively. | Unisex | English |
| Spaz | For a spazy kitty | Unisex | English |
| Speedy | Rapid motion, swift. | Unisex | English |
| Spider | An eight legged insect | Unisex | English |
| Spike | A long, thick sharp-pointed piece of wood or metal | Male | English |
| Spirit | Part of the human being associated with the mind. Vigorous or animated state - spirited. Also distilled alcohol. | Unisex | English |
| Spot | After Data's cat on Star Trek: The Next Generation | Unisex | English |