| burdensome(adjective, hard, difficult, complex) |
| complex(adjective, hard, difficult) |
| complicated(adjective, hard, difficult, complex) |
| knotty(adjective, hard, difficult, complex) |
| punishing(adjective, hard, difficult, complex, troublesome) |
| rugged(adjective, hard, difficult, complex) |
| settled(adjective, strain, firmness, labour, hardiness) |
| stressful(adjective, hard, difficult, complex) |
| stubborn(adjective, hard, difficult, complex, rigid) |
| thorny(adjective, hard, difficult, complex) |
| toilsome(adjective, hard, difficult, complex) |
| tense(adjective, close, hard, firm, difficult) |
| conservative(adjective, strain, firmness, labour, hardiness) |
| cruel(adjective, hard, difficult, complex) |
| durable(adjective, strain, firmness, labour, hardiness) |
| enduring(adjective, close, strain, firmness, labour) |
| grinding(adjective, hard, difficult, complex) |
| impregnable(adjective, strain, firm, true, firmness) |
| lasting(adjective, strain, firmness, labour, hardiness) |
| permanent(adjective, strain, firmness, labour, hardiness) |