| sentience | Capacity for sensation or sense-perception. |
| sentient | Possessing the power of sense or sense-perception. |
| sentinel | Any guard or watch stationed for protection. |
| separable | Capable of being disjoined or divided. |
| separate | To take apart. |
| separatist | A seceder. |
| septennial | Recurring every seven years. |
| sepulcher | A burial-place. |
| sequacious | Ready to be led. |
| sequel | That which follows in consequence of what has previously happened. |
| sequence | The order in which a number or persons, things, or events follow one another in space or time. |
| sequent | Following in the order of time. |
| sequester | To cause to withdraw or retire, as from society or public life. |
| sequestrate | To confiscate. |
| sergeant | A non-commissioned military officer ranking next above a corporal. |
| sergeant-at-arms | An executive officer in legislative bodies who enforces the orders of the presiding officer. |
| sergeant-major | The highest non-commissioned officer in a regiment. |
| service | Any work done for the benefit of another. |
| serviceable | Durable. |
| servitude | Slavery. |
| severance | Separation. |
| severely | Extremely. |
| sextet | A band of six singers or players. |
| sextuple | Multiplied by six. |
| sheer | Absolute. |
| shiftless | Wanting in resource, energy, or executive ability. |
| shrewd | Characterized by skill at understanding and profiting by circumstances. |
| shriek | A sharp, shrill outcry or scream, caused by agony or terror. |
| shrinkage | A contraction of any material into less bulk or dimension. |
| shrivel | To draw or be drawn into wrinkles. |
| shuffle | A mixing or changing the order of things. |
| sibilance | A hissing sound. |
| sibilant | Made with a hissing sound. |
| sibilate | To give a hissing sound to, as in pronouncing the letter s. |
| sidelong | Inclining or tending to one side. |
| sidereal | Pertaining to stars or constellations. |
| siege | A beleaguerment. |
| significance | Importance. |
| significant | Important, especially as pointing something out. |
| signification | The meaning conveyed by language, actions, or signs. |
| similar | Bearing resemblance to one another or to something else. |
| simile | A comparison which directs the mind to the representative object itself. |
| similitude | Similarity. |
| simplify | To make less complex or difficult. |
| simulate | Imitate. |
| simultaneous | Occurring, done, or existing at the same time. |
| sinecure | Any position having emoluments with few or no duties. |
| singe | To burn slightly or superficially. |
| sinister | Evil. |
| sinuosity | The quality of curving in and out. |