| dire(adjective, hard, difficult, complex, painful) |
| weighty(adjective, hard, tough, difficult, honest) |
| acute(adjective, strong, great, severe, sharp) |
| rigorous(adjective, strong, hard, tough, correct) |
| nasty(adjective, bad, hard, tough, difficult) |
| rugged(adjective, strong, hard, tough, rough) |
| extreme(adjective, strong, hard, great, tough) |
| punishing(adjective, hard, difficult, harsh, complex) |
| unbearable(adjective, hard, difficult, complex, painful) |
| laborious(adjective, hard, tough, rough, difficult) |
| taxing(adjective, hard, tough, difficult, harsh) |
| toilsome(adjective, hard, tough, difficult, harsh) |
| inflexible(adjective, strong, hard, tough, rough) |
| grinding(adjective, hard, difficult, harsh, pain) |
| tight(adjective, hard, difficult, complex, rigid) |
| biting(verb, adjective, mean, strong, cool) |
| knotty(adjective, hard, difficult, violent, complex) |
| stubborn(adjective, appearance, strong, hard, tough) |
| thorny(adjective, hard, difficult, complex, problematic) |
| trying(adjective, hard, difficult, heavy, complex) |