| Solution | Length | |
|---|---|---|
| 3 letters | ||
| der | 3 | |
| aft | 3 | |
| 4 letters | ||
| rear | 4 | |
| grim | 4 | |
| arco | 4 | |
| hard | 4 | |
| imus | 4 | |
| dour | 4 | |
| iron | 4 | |
| aust | 4 | |
| tush | 4 | |
| back | 4 | |
| tail | 4 | |
| ship | 4 | |
| 5 letters | ||
| rough | 5 | |
| isaac | 5 | |
| stiff | 5 | |
| tight | 5 | |
| rigid | 5 | |
| tough | 5 | |
| grave | 5 | |
| glare | 5 | |
| harsh | 5 | |
| 6 letters | ||
| fierce | 6 | |
| strict | 6 | |
| unkind | 6 | |
| severe | 6 | |
| steely | 6 | |
| rugged | 6 | |
| flinty | 6 | |
| 7 letters | ||
| austere | 7 | |
| pungent | 7 | |
| spartan | 7 | |
| serious | 7 | |
| reverse | 7 | |
| puritan | 7 | |
| unmoved | 7 | |
| prudish | 7 | |
| 8 letters | ||
| rear-end | 8 | |
| ungiving | 8 | |
| scathing | 8 | |
| rigorous | 8 | |
| rearward | 8 | |
| 9 letters | ||
| stringent | 9 | |
| tailpiece | 9 | |
| unsparing | 9 | |
| unbending | 9 | |
| 10 letters | ||
| forbidding | 10 | |
| UNYIELDING | 10 | |
| UNAFFECTED | 10 | |
| relentless | 10 | |
| 11 letters | ||
| unalterable | 11 | |
| unrelenting | 11 | |
| 12 letters | ||
| UNCHANGEABLE | 12 | |
| 14 letters | ||
| UNCOMPROMISING | 14 | |