| doubtful(uncertain, vague, unclear) |
| dubious(uncertain, vague, unclear) |
| enigmatically |
| entangled(hard, tricky, complicated, caught, multiplex) |
| esoteric(hard, obscure, delicate, strange, complex) |
| fathomless |
| formidable(hard, delicate, complex, tricky, complicated) |
| hard to explain(expression, idiom, hard, delicate, complex) |
| hard to solve(expression, idiom, hard, delicate, complex) |
| hidden(hard, solid, strange, dense, tricky) |
| inconclusive(obscure, uncertain, vague, unclear, indefinite) |
| indecipherable |
| indefinite(obscure, uncertain, vague, unclear, equivocal) |
| indistinct(uncertain, vague, unclear) |
| inexplicable(adjective, hard, delicate, solid, strange) |
| inexplicit(adjective, obscure, uncertain, vague, unclear) |
| insoluble |
| intricate(hard, tricky, complicated, caught, multiplex) |
| involved(hard, tricky, complicated, caught, multiplex) |
| loose(hard, delicate, complex, tricky, complicated) |