| robust(adjective, strong, hard, tough, strain) |
| stabile(adjective, strain, firmness, labour, hardiness) |
| staying(adjective, strain, firmness, labour, hardiness) |
| stout(adjective, strain, firmness, labour, hardiness) |
| sustained(adjective, strain, firmness, labour, hardiness) |
| defensive(adjective, strain, firmness, labour, hardiness) |
| immune(adjective, strain, firmness, labour, hardiness) |
| impregnable(adjective, strain, firmness, labour, hardiness) |
| resilient(adjective, strong, strain, stiff, firmness) |
| resist(adjective, strain, firmness, labour, hardiness) |
| stringent(adjective, hard, tough, severe, rough) |
| substantial(adjective, strain, firmness, labour, hardiness) |
| well-balanced(adjective, strain, firmness, even, labour) |
| withstanding(adjective, strong, strain, stiff, firmness) |
| hidebound(adjective, moderate, severe, determined, resolute) |
| inelastic(adjective, hard, tough, severe, firm) |
| set in stone(expression, adjective, idiom, mean, hard) |
| exact(adjective, correct, severe, solid, proper) |
| iron(adjective, mean, strong, hard, tough) |
| precise(adjective, hard, correct, severe, rough) |