| tough(adjective, action, strong, hard, sound) |
| rough(adjective, action, calm, quiet, strong) |
| hard(adjective, strong, tough, severe, continue) |
| strong(adjective, hard, sound, tough, fit) |
| severe(adjective, strong, hard, tough, rough) |
| difficult(adjective, hard, severe, evil, rough) |
| arduous(adjective, hard, severe, rough, difficult) |
| knotty(adjective, hard, severe, difficulty, difficult) |
| hefty(adjective, hard, difficult, complex) |
| laborious(adjective, hard, severe, rough, difficult) |
| burly(adjective, hard, difficult, complex) |
| sturdy(adjective, strong, hard, sound, tough) |
| thorny(adjective, hard, difficulty, difficult, complex) |
| harsh(adjective, strong, hard, smooth, tough) |
| trying(adjective, hard, difficulty, difficult, complex) |
| burdensome(adjective, hard, severe, rough, difficult) |
| complicated(adjective, hard, difficulty, difficult, complex) |
| intricate(adjective, hard, difficulty, difficult, complex) |
| tricky(adjective, hard, difficult, delicate, uncertain) |
| complex(adjective, hard, difficult) |