| Term | Definition |
| self-assured | sure |
| self-effacing | unassuming |
| sequester | isolate |
| serendipity | chance |
| serenity | calmness |
| sermonize | lecture |
| serpentine | winding |
| setback | obstacle |
| shallow | not showing serious thought |
| shattering | crushing |
| shoddy | inferior |
| shun | avoid |
| sierra | range |
| simulate | assume |
| simultaneous | coinciding |
| sinecure | easy job |
| skeptic | disbeliever |
| skepticism | doubt |
| skimp | pinch |
| slight | insult |
| slipshod | careless |
| slothful | slack |
| smug | self-satisfied |
| sobriety | sanity |
| solace | comfort or relief |
| solemn | silent |
| solicitous | anxious |
| solicitude | care |
| sonorous | having a full deep sound |
| soothe | calm |
| sophistry | use of sophism |
| sophomoric | silly and childish |
| soporific | sleep-inducing |
| sovereignty | independence |
| spare | reserve |
| sparingly | economically |
| spate | flood |
| specter | shadow |
| speculation | guess |
| speculative | theoretical |
| spellbinding | captivating |
| sporadic | irregular |
| spurious | counterfeit |
| squalor | dirt |
| squander | waste |
| squadered | misused |
| squelch | crush |
| stagnate | to stay the time and not grow or develop |
| stagnation | inaction |
| staid | serious, boring and old-fashioned |
| stalwart | loyal |
| standoffish | unfriendly |
| stasis | stoppage |
| stature | status |
| steadfast | loyal |
| stealthy | sneaky |
| stem | control |
| stentorian | loud |