| restive |
| rheumatic(adjective, hard, firm, solid, tense) |
| rock-ribbed(adjective, determined, resolute, uncompromising, unshakeable) |
| set(adjective, hard, firm, solid, stiff) |
| set in stone(expression, adjective, idiom, tough, severe) |
| single-minded(adjective, tough, severe, firm, harsh) |
| solid(adjective, hard, firm, stiff, tense) |
| solidified(adjective, hard, firm, solid, tense) |
| standing pat(expression, adjective, tough, firm, distant) |
| starched(adjective, hard, firm, solid, stiff) |
| starchy(adjective, hard, firm, solid, tense) |
| stark(adjective, hard, firm, solid, tense) |
| stiff as a board(expression, adjective, idiom, firm, solid) |
| stony(adjective, hard, firm, solid, stiff) |
| strong-willed(adjective, determined, resolute, uncompromising, unshakeable) |
| stroppy |
| taut(adjective, hard, firm, solid, stiff) |
| tense(adjective, hard, firm, solid, stiff) |
| thick(adjective, hard, firm, solid, stiff) |
| thickened(adjective, hard, firm, solid, tense) |