| soupcon | A very small quantity or trace of something | |
| sordid | involving ignoble actions and motives; arousing moral distaste and contempt; dirty or squalid | |
| soporific | Tending to induce drowsiness or sleep | |
| sophomoric | Pertaining to or characteristic of a sophomore; considered to be overconfident, conceited, and exhibiting a lack of maturity | |
| somnolent | sleepy; drowsy | |
| solipsistic | Relating to the philosophical theory that only the self is real and that the self cannot be aware of anything else except its own existence | |
| solidarity | Unity or agreement of feeling or action, especially among individuals with a common interest; mutual support within a group | |
| solicitous | Showing concern or care for someone's health, happiness, or welfare | |
| solecism | A grammatical mistake or error in language | |
| sojourn | A temporary stay at a place | |