| multiple(adjective, hard, difficult, involved, number) |
| tough(adjective, hard, difficult) |
| hard to understand(expression, adjective, idiom, hard, difficult) |
| multiplex(noun, adjective, hard, difficult, involved) |
| rough(adjective, hard, difficult, tedious, demanding) |
| toilsome(adjective, hard, difficult) |
| disturbing(adjective, hard, difficult) |
| involute(adjective, hard, simple, difficult) |
| rugged(adjective, hard, difficult) |
| severe(adjective, hard, difficult) |
| problematic(adjective, hard, difficult, delicate, awkward) |
| oppressive(adjective, hard, difficult, tedious, demanding) |
| perplexed(adjective, hard, difficult, complexity) |
| profound(adjective, hard, difficult, tedious, demanding) |
| sensitive(adjective, hard, difficult, delicate, awkward) |
| sinuous(adjective, hard, difficult) |
| sticky(adjective, hard, difficult) |
| stressful(adjective, hard, difficult) |
| structure(noun, organization, form, design, system) |
| trying(adjective, hard, difficult, tricky, problematic) |