| Solution | Length | |
|---|---|---|
| 5 letters | ||
| stiff | 5 | |
| setin | 5 | |
| stern | 5 | |
| tough | 5 | |
| rigid | 5 | |
| 6 letters | ||
| steely | 6 | |
| stable | 6 | |
| lockin | 6 | |
| 7 letters | ||
| unmoved | 7 | |
| uniform | 7 | |
| 8 letters | ||
| ungiving | 8 | |
| rigorous | 8 | |
| resolute | 8 | |
| stubborn | 8 | |
| 9 letters | ||
| UNVARYING | 9 | |
| merciless | 9 | |
| unpliable | 9 | |
| unbending | 9 | |
| unaltered | 9 | |
| immutable | 9 | |
| 10 letters | ||
| relentless | 10 | |
| UNCHANGING | 10 | |
| UNAFFECTED | 10 | |
| UNYIELDING | 10 | |
| inexorable | 10 | |
| 11 letters | ||
| UNREMITTING | 11 | |
| undeviating | 11 | |
| UNAVOIDABLE | 11 | |
| IMPREGNABLE | 11 | |
| unrelenting | 11 | |
| irrevocable | 11 | |
| hardandfast | 11 | |
| 12 letters | ||
| irreversible | 12 | |
| UNCHANGEABLE | 12 | |
| unreturnable | 12 | |
| 13 letters | ||
| unsusceptible | 13 | |
| 14 letters | ||
| UNCOMPROMISING | 14 | |