| tough(adjective, mean, strong, hard, severe) |
| unmerciful(adjective, mean, hard, tough, severe) |
| inhuman(adjective, animal, mean, hard, tough) |
| persevering(adjective, strong, tough, firm, determined) |
| pertinacious(adjective, strong, tough, firm, energetic) |
| rigorous(adjective, strong, hard, tough, severe) |
| set in stone(expression, adjective, idiom, mean, hard) |
| brutal(adjective, mean, strong, severe, evil) |
| callous(adjective, mean, hard, severe, evil) |
| eternal(adjective, continue, pause, steady, persistent) |
| heartless(adjective, mean, hard, severe, evil) |
| hidebound(adjective, severe, determined, resolute, persistent) |
| indomitable(adjective, strong, hard, tough, determined) |
| uninterrupted(adjective, continue, steady, persistent, constant) |
| unsparing(adjective, mean, strong, hard, tough) |
| unswayable(adjective, determined, resolute, rigid, obstinate) |
| business-minded |
| dour(adjective, close, hard, severe, sharp) |
| ferocious(adjective, animal, mean, strong, severe) |
| hanging tough(expression, adjective, mean, hard, determined) |