| robust(adjective, strong, sound, secure, tough) |
| rugged |
| sage(adjective, reason, sane) |
| sanguine(adjective, strong, easy, solid, certain) |
| sapient(adjective, reason, sane) |
| self-assured(adjective, strong, easy, solid, certain) |
| self-confident(adjective, strong, easy, solid, certain) |
| set in stone(expression, idiom, calm, strong, substantial) |
| shoo-in(adjective, strong, easy, solid, certain) |
| sinewy(adjective, strong, sound, tough, solid) |
| solid as a rock(expression, idiom, calm, strong, substantial) |
| stabile(calm, strong, solid, steady, substantial) |
| stalwart(adjective, calm, strong, sound, secure) |
| stark(adjective, strong, sound, tough, solid) |
| stationary(calm, strong, secure, solid, steady) |
| staying put(expression, calm, strong, solid, substantial) |
| strapping(adjective, strong, sound, tough, solid) |
| substantiated |
| sufficient |
| sure thing(expression, adjective, strong, easy, solid) |