| top secret(expression, clandestine, underground, undisclosed) |
| transcendental(strange, supernatural, spiritual, mystical, inexplicable) |
| transmundane(obscure, deep, mysterious, weird) |
| uncommon(adjective, unusual, strange, special, different) |
| under wraps(expression, clandestine, underground, undisclosed) |
| undisclosed(obscure, unknown, clandestine, underground, unrevealed) |
| unfamiliar(unusual, special, rare) |
| unusual(adjective, strange, special, rare, unfathomable) |
| Delphian(adjective, evil, obscure, deep, wise) |
| abnormal(adjective, unusual, special, rare) |
| abstract |
| acroamatic(obscure, complex, deep, mysterious, weird) |
| anagogic(adjective, evil, deep, mysterious, secret) |
| backdoor(adjective, obscure, deep, intimate, mysterious) |
| censored |
| closed |
| confusing |
| covered(obscure, unknown, clandestine, underground, undisclosed) |
| cryptical |
| curious(unusual, strange, special, rare, inexplicable) |