| frustrating(verb, adjective, hindering) |
| unaccountable(adjective, obscure, solid, strange, mysterious) |
| unclear(adjective, hard, obscure, difficult, loose) |
| abstruse(adjective, hard, obscure, difficult, dark) |
| ambiguous |
| disconcerting(adjective, complicated, knotty, puzzling, confusing) |
| hard(tough, obscure, solid, awkward, dense) |
| impenetrable(adjective, obscure, solid, deep, mysterious) |
| inscrutable(adjective, solid, strange, dense, unfathomable) |
| opaque(adjective, hard, obscure, difficult, unclear) |
| recondite |
| thorny(adjective, difficult, delicate, complex, tricky) |
| complicated(adjective, hard, difficult, complex, awkward) |
| confused |
| elusive(adjective, mysterious, evasive) |
| equivocal(adjective, obscure, difficult, dark, strange) |
| indecipherable(adjective, unintelligible) |
| indefinite |
| insoluble(adjective, unable, answered) |
| involved(adjective, hard, difficult, complex, awkward) |