| Solution | Length | |
|---|---|---|
| 3 letters | ||
| set | 3 | |
| 4 letters | ||
| taut | 4 | |
| true | 4 | |
| iron | 4 | |
| 5 letters | ||
| stern | 5 | |
| rigid | 5 | |
| stiff | 5 | |
| rocky | 5 | |
| right | 5 | |
| tough | 5 | |
| 6 letters | ||
| unbent | 6 | |
| steely | 6 | |
| severe | 6 | |
| formal | 6 | |
| strict | 6 | |
| steady | 6 | |
| smooth | 6 | |
| unkind | 6 | |
| 7 letters | ||
| unmoved | 7 | |
| upright | 7 | |
| adamant | 7 | |
| unbowed | 7 | |
| settled | 7 | |
| precise | 7 | |
| puritan | 7 | |
| staunch | 7 | |
| 8 letters | ||
| puristic | 8 | |
| unshaken | 8 | |
| hardline | 8 | |
| ungiving | 8 | |
| unbroken | 8 | |
| straight | 8 | |
| obdurate | 8 | |
| stubborn | 8 | |
| stalwart | 8 | |
| vertical | 8 | |
| rigorous | 8 | |
| 9 letters | ||
| ROCKBOUND | 9 | |
| steadfast | 9 | |
| unpliable | 9 | |
| 10 letters | ||
| UNYIELDING | 10 | |
| inexorable | 10 | |
| UNAFFECTED | 10 | |
| relentless | 10 | |
| UNSWERVING | 10 | |
| 11 letters | ||
| puritanical | 11 | |
| UNFLAPPABLE | 11 | |
| straitlaced | 11 | |
| streamlined | 11 | |
| undeviating | 11 | |
| UNDISTORTED | 11 | |
| unalterable | 11 | |
| uncompliant | 11 | |
| rectilinear | 11 | |
| PROCRUSTEAN | 11 | |
| unrelenting | 11 | |
| 12 letters | ||
| UNCHANGEABLE | 12 | |
| recalcitrant | 12 | |
| 13 letters | ||
| single-minded | 13 | |
| STRAIGHTLACED | 13 | |
| UNINTERRUPTED | 13 | |
| 14 letters | ||
| UNCOMPROMISING | 14 | |
| UNAPPROACHABLE | 14 | |
| 15 letters | ||
| UNCOMMUNICATIVE | 15 | |