| esoteric(adjective, hard, evil, difficult, complex) |
| hard to understand(expression, adjective, idiom, hard, difficult) |
| impossible(adjective, hard, difficulty, difficult, complex) |
| inextricable(adjective, hard, difficult, complex, complexity) |
| multiplex(adjective, hard, difficult, complex) |
| painful(adjective, hard, difficult, complex) |
| profound(adjective, hard, difficult, complex) |
| serious(adjective, hard, difficult, complex, awkward) |
| tangly(adjective, hard, difficult, complex) |
| toilful(adjective, hard, difficult, complex, awkward) |
| convoluted(adjective, simple, obscure, difficulty, difficult) |
| multiple(adjective, hard, difficult, complex) |
| operose(adjective, hard, difficult, complex, awkward) |
| precarious(adjective, hard, difficult, complex) |
| sheer(adjective, hard, fancy, difficult, delicate) |
| stubborn(adjective, hard, difficulty, difficult, complex) |
| troubled(adjective, upset, hard, difficult, complex) |
| tangled(verb, adjective, hard, simple, obscure) |
| tortuous(adjective, obscure, difficult, complex, sophisticated) |
| perplexing(adjective, hard, obscure, difficult, delicate) |