| unshakable(adjective, mean, hard, secure, firm) |
| hard-nosed(adjective, mean, clear, hard, secure) |
| unbendable(adjective, resist, determined, resolute, persistent) |
| severe(adjective, clear, hard, tough, severe) |
| adamantine(adjective, tough, resist, determined, resolute) |
| steadfast(adjective, clear, secure, tough, severe) |
| tough(adjective, mean, clear, hard, severe) |
| implacable(adjective, mean, hard, harsh, resist) |
| stern(adjective, severe, rough, harsh, determined) |
| strict(adjective, hard, tough, severe, rough) |
| unwavering(adjective, determined, fixed, resolute, purpose) |
| hard(adjective, mean, severe, rough, difficult) |
| grim(adjective, severe, harsh, resist, cruel) |
| set in stone(expression, adjective, idiom, mean, hard) |
| dogged(adjective, mean, hard, firm, harsh) |
| rigorous(adjective, hard, severe, rough, difficult) |
| standing pat(expression, adjective, tough, firm, determined) |
| unswayable(adjective, tough, firm, determined, distant) |
| tenacious(adjective, tough, firm, determined, resolute) |
| harsh(adjective, mean, hard, severe, rough) |