| seasoned(adjective, strong, hard, solid, stiff) |
| secure(adjective, strong, sound, tough, solid) |
| sedate(adjective, calm, cool, steady, unaffected) |
| self-possessed(adjective, calm, cool, steady, tranquil) |
| self-satisfied(adjective, calm, cool, steady, tranquil) |
| set in stone(expression, adjective, idiom, tough, firm) |
| severe(adjective, tough, firm, harsh, fixed) |
| sinewy(adjective, strong, hard, sound, tough) |
| single-minded(adjective, tough, firm, fixed, serious) |
| smug(adjective, calm, cool, steady, tranquil) |
| sound(adjective, strong, tough, solid, heavy) |
| stable(adjective, strong, sound, tough, solid) |
| standing pat(expression, adjective, tough, firm, distant) |
| stark(adjective, strong, sound, tough, solid) |
| staunch(adjective, strong, sound, tough, solid) |
| steady(adjective, calm, strong, cool, sound) |
| steeled(adjective, strong, hard, solid, stiff) |
| stern(adjective, tough, severe, harsh, cruel) |
| stiff(adjective, set, strong, hard, tough) |
| stiff upper lip(expression, adjective, idiom, calm, cool) |