| hard(adjective, mean, strong, tough, severe) |
| continual(adjective, continue, determined, persistent, constant) |
| iron(adjective, mean, strong, hard, tough) |
| pitiless(adjective, animal, mean, hard, tough) |
| unappeasable(adjective, mean, severe, harsh, cruel) |
| unwavering(adjective, firm, determined, steady, resolute) |
| continuous(adjective, continue, steady, persistent, constant) |
| incessant(adjective, continue, determined, steady, persistent) |
| resolved(adjective, determined, resolution, resolute, persistent) |
| savage(adjective, animal, mean, strong, hard) |
| strict(adjective, strong, hard, tough, severe) |
| unceasing(adjective, continue, steady, persistent, constant) |
| unflinching(adjective, mean, severe, firm, harsh) |
| austere(adjective, appearance, mean, strong, hard) |
| ceaseless(adjective, continue, steady, persistent, constant) |
| exacting(adjective, severe, persistent, severity, obstinate) |
| fierce(adjective, animal, mean, hard, tough) |
| perpetual(adjective, continue, determined, steady, persistent) |
| steady(adjective, firm, determined, resolution, resolute) |
| stiff-necked(adjective, mean, strong, hard, tough) |