| Solution | Length | |
|---|---|---|
| 4 letters | ||
| hard | 4 | |
| iron | 4 | |
| 5 letters | ||
| tough | 5 | |
| rocky | 5 | |
| stony | 5 | |
| solid | 5 | |
| stern | 5 | |
| rigid | 5 | |
| stiff | 5 | |
| 6 letters | ||
| unfelt | 6 | |
| steely | 6 | |
| severe | 6 | |
| seared | 6 | |
| 7 letters | ||
| adamant | 7 | |
| puritan | 7 | |
| callous | 7 | |
| 8 letters | ||
| puristic | 8 | |
| stubborn | 8 | |
| rigorous | 8 | |
| hardened | 8 | |
| 9 letters | ||
| untouched | 9 | |
| unfeeling | 9 | |
| hardnosed | 9 | |
| ROCKBOUND | 9 | |
| obstinate | 9 | |
| reprobate | 9 | |
| unbending | 9 | |
| unnatural | 9 | |
| resistant | 9 | |
| shameless | 9 | |
| steadfast | 9 | |
| tenacious | 9 | |
| 10 letters | ||
| relentless | 10 | |
| unmerciful | 10 | |
| unsoftened | 10 | |
| IMPENITENT | 10 | |
| headstrong | 10 | |
| UNYIELDING | 10 | |
| INSENSIBLE | 10 | |
| 11 letters | ||
| PROCRUSTEAN | 11 | |
| uncompliant | 11 | |
| unrepentant | 11 | |
| straitlaced | 11 | |
| unemotional | 11 | |
| puritanical | 11 | |
| unrelenting | 11 | |
| 12 letters | ||
| thick-witted | 12 | |
| unresponsive | 12 | |
| unperceptive | 12 | |
| 13 letters | ||
| unsympathetic | 13 | |
| STRAIGHTLACED | 13 | |
| single-minded | 13 | |
| Thick-skinned | 13 | |
| 14 letters | ||
| UNCOMPROMISING | 14 | |
| 15 letters | ||
| uncompassionate | 15 | |