| spooky |
| unfathomable(adjective, hard, solid, strange, dense) |
| unintelligible(adjective, hard, obscure, delicate, solid) |
| abstract(hard, delicate, complex, tricky, complicated) |
| alchemistic |
| anagogic(supernatural, spiritual, mystical) |
| astrological |
| backdoor(obscure, deep, unknown, clandestine, underground) |
| baffling(hard, delicate, solid, strange, complex) |
| camouflaged(obscure, unknown, clandestine, underground, undisclosed) |
| clear as dishwater(expression, obscure, uncertain, vague, unclear) |
| close(obscure, solid, unknown, dense, underground) |
| clouded(obscure, unknown, indefinite, equivocal, clandestine) |
| concealed |
| confounding(hard, difficult, delicate, complex, tricky) |
| conspiratorial(obscure, unknown, clandestine, underground, undisclosed) |
| covered(obscure, unknown, clandestine, underground, undisclosed) |
| covert(strange, clandestine, underground, undisclosed, inexplicable) |
| curious |
| deep(hard, obscure, delicate, complex, unknown) |