| involved(adjective, hard, difficult, complex, awkward) |
| knotty(adjective, hard, difficult, complex, awkward) |
| leaden(adjective, hard, difficult, complex) |
| painful(adjective, hard, difficult, complex) |
| rugged(adjective, hard, difficult, complex, awkward) |
| serious(adjective, hard, difficult, complex, awkward) |
| sticky(adjective, hard, difficult, complex, awkward) |
| toilful(adjective, hard, difficult, complex, awkward) |
| grave(adjective, hard, difficult, complex) |
| ponderous(adjective, hard, difficult, complex) |
| profound(adjective, hard, difficult, complex) |
| tricky(adjective, hard, difficult, complex, awkward) |
| grueling(adjective, hard, tough, severe, difficult) |
| gruelling |
| heavy(adjective, hard, difficult, harsh, heavy) |
| effortful(adjective, hard, severe, rough, difficult) |
| onerous(adjective, hard, difficult, heavy, cruel) |
| strenuous(adjective, strong, hard, rough, difficult) |
| demanding(adjective, hard, difficult, harsh, heavy) |
| exacting(adjective, hard, difficult, harsh, heavy) |