| Name | Meaning | Gender | Origin |
|---|
| Rebel | One that resists of defies authority | Unisex | English |
| Rex | King | Male | Latin |
| Riley | Rye clearing | Male | English |
| Rocky | Battle cry | Male | Germanic |
| Rogue | | Unisex | Hebrew |
| Rosie | Rose | Female | Latin |
| Roxy | Star | Female | Persian |
| Ruby | Red | Female | Latin |
| Rufus | Red | Male | Latin |
| Rusty | Rusty, full of rust | Unisex | American English |
| Sabre | | Unisex | Hebrew |
| Sadie | Princess | Female | Hebrew |
| Sam | He is called god | Male | Hebrew |
| Sammy | His name is God | Unisex | Hebrew |
| Sandy | Defending men | Male | Greek |
| Sarge | Noncommissioned Army or Air Force rank | Unisex | English |
| Sasha | Defending men | Unisex | Greek |
| Scout | Observer | Unisex | American English |
| Shadow | Shadow | Unisex | English |
| Shorty | Of less than average size | Unisex | English |
| Smoky | | Unisex | Hebrew |
| Sophie | Wisdom | Female | Greek |
| Sparky | Animated, lively. | Unisex | English |
| Spike | A long, thick sharp-pointed piece of wood or metal | Male | English |
| Spot | After Data's cat on Star Trek: The Next Generation | Unisex | English |
| Squirt | Slang for a small person | Unisex | English |
| Sugar | A sweet powder from sugar cane. Slang for sweetheart. | Female | English |
| Suger | | Unisex | Hebrew |
| Tank | A large metal container. A heavily armed combat vehicle | Unisex | English |
| T-bone | A thick steak containing a T shaped bone. | Unisex | English |