| Solution | Length | |
|---|---|---|
| 4 letters | ||
| rare | 4 | |
| 6 letters | ||
| opaque | 6 | |
| gnomic | 6 | |
| unique | 6 | |
| virgin | 6 | |
| untold | 6 | |
| sealed | 6 | |
| secret | 6 | |
| 7 letters | ||
| STIFLED | 7 | |
| cryptic | 7 | |
| unknown | 7 | |
| strange | 7 | |
| 8 letters | ||
| puzzling | 8 | |
| somalian | 8 | |
| skislope | 8 | |
| unspoken | 8 | |
| wondrous | 8 | |
| ulterior | 8 | |
| profound | 8 | |
| striking | 8 | |
| 9 letters | ||
| unplumbed | 9 | |
| wonderful | 9 | |
| upsetting | 9 | |
| mona lisa | 9 | |
| smothered | 9 | |
| uncharted | 9 | |
| UNEXPOSED | 9 | |
| unuttered | 9 | |
| uncertain | 9 | |
| untouched | 9 | |
| RECONDITE | 9 | |
| unbeknown | 9 | |
| 10 letters | ||
| restricted | 10 | |
| unheard-of | 10 | |
| unfathomed | 10 | |
| unfamiliar | 10 | |
| neandertal | 10 | |
| SPHINXLIKE | 10 | |
| MYSTERIOUS | 10 | |
| PRODIGIOUS | 10 | |
| SUPPRESSED | 10 | |
| remarkable | 10 | |
| top-secret | 10 | |
| stupendous | 10 | |
| UNEXPLORED | 10 | |
| UNKNOWABLE | 10 | |
| unrevealed | 10 | |
| 11 letters | ||
| BEWILDERING | 11 | |
| unutterable | 11 | |
| sensational | 11 | |
| UNDISCLOSED | 11 | |
| unsuspected | 11 | |
| UNEXPLAINED | 11 | |
| UNPERCEIVED | 11 | |
| UNDER WRAPS | 11 | |
| problematic | 11 | |
| 12 letters | ||
| UNIDENTIFIED | 12 | |
| unclassified | 12 | |
| UNDISCOVERED | 12 | |
| unimaginable | 12 | |
| 13 letters | ||
| PROBLEMATICAL | 13 | |
| unprecedented | 13 | |
| undisclosable | 13 | |
| 14 letters | ||
| undiscoverable | 14 | |
| decimal system | 14 | |