| Hidden |
| Occult |
| Secret |
| Cryptic |
| Obscure |
| Abstruse |
| Esoteric |
| Recondite |
| Cabalistic |
| Recherché |
| Mysterious |
| Hard to know |
| Recherché |
| Known by few |
| Impenetrable |
| Gotten by few |
| An acre (anag) |
| Incomprehensible |
| Like cult rituals |
| Like much tax law |
| Known by very few |
| Understood by few |
| Not commonly known |
| Mysterious to most |
| Hard to understand |
| Like secret rituals |
| Like the fine print |
| Tough to understand |
| Not generally known |
| Known by only a few |
| Select, as knowledge |
| Known by a select few |
| Not widely understood |
| Antonym of "well-known |
| Known only by insiders |
| Like federal tax laws? |
| Understood by very few |
| Like little-known facts |
| Difficult to understand |
| Secret, mysterious, etc. |
| Understood only by a few |
| Understood by only a few |
| Far from general knowledge |
| Requiring secret knowledge |
| Apprehended by a small group |
| Like election laws, typically |
| Like Stonehenge's true purpose, e.g. |