| troublesome(adjective, tough, severe, difficult, awkward) |
| zippy(adjective, strong, tough, energetic, powerful) |
| Herculean(adjective, strong, tough, severe, difficult) |
| back-breaking |
| enterprising(adjective, activity, strong, tough, smart) |
| enthusiastic(adjective, determined, active, vigorous, resolute) |
| indefatigable(adjective, strong, moving, difficult, energetic) |
| knotty(adjective, hard, severe, rough, difficult) |
| mettlesome(adjective, strong, tough, intense, energetic) |
| murderous(adjective, difficult) |
| red-blooded(adjective, strong, tough, intense, energetic) |
| stiff(adjective, tough, severe, difficult, painful) |
| stressful(state, feeling, stress) |
| thorny(adjective, difficult, embarrassing) |
| tight(adjective, difficult) |
| tricky(adjective, difficult, awkward, demanding, irritating) |
| punishing |
| complex(adjective, difficult) |
| fervent(adjective, difficult, vigorous, stressful) |
| finicky(adjective, difficult, thorough, meticulous, painstaking) |