| immovable(adjective, strong, hard, tough, cruel) |
| implacable(adjective, strong, hard, tough, resist) |
| grim(adjective, strong, hard, tough, resist) |
| determined(adjective, strong, hard, tough, severe) |
| resolute(adjective, hard, determined, rigid, strict) |
| steely(adjective, strong, hard, tough, firm) |
| stony(adjective, firm, stiff, rigid, stubborn) |
| iron(adjective, set, strong, hard, tough) |
| stern(adjective, determined, resolute, uncompromising, unshakeable) |
| stiff(adjective, set, firm, harsh, determined) |
| rocky(adjective, set, firm, stiff, compact) |
| uncompliant(adjective, tough, firm, resist, determined) |
| fixed(adjective, tough, severe, determined, resolute) |
| incompliant(adjective, resist, determined, resolute, persistent) |
| obstinate(adjective, cruel, determined, resolute, pitiless) |
| set(adjective, severe, firm, harsh, determined) |
| brassbound(adjective, resist, determined, resolute, persistent) |
| die-hard(adjective, resist, determined, resolute, persistent) |
| hardheaded(adjective, strong, hard, tough, firm) |
| pat(adjective, determined, resolute, uncompromising, unshakeable) |