| perpetual(adjective, quality, strain, steady, regular) |
| rigid(adjective, state, secure, strain, firm) |
| unalterable(adjective, strong, secure, strain, flat) |
| tight(adjective, close, strong, hard, secure) |
| settled(adjective, strong, secure, easy, strain) |
| stabile(adjective, calm, direct, smooth, right) |
| conservative(adjective, reasonable, moderate, strain, mild) |
| quiescent(adjective, calm, secure, strain, still) |
| robust(adjective, strong, sound, complete, secure) |
| long-standing(adjective, strain, firmness, labour, hardiness) |
| resistant(adjective, strain, firmness, labour, hardiness) |
| unyielding(adjective, strong, hard, sound, secure) |
| rock-solid(adjective, hard, strain, firmness, compact) |
| sustained(adjective, strain, firmness, persistent, continuous) |
| tenable(adjective, strain, firmness, labour, hardiness) |
| well-balanced(adjective, calm, sound, strain, rational) |
| immune(adjective, strain, firmness, safe, labour) |
| impregnable(adjective, strain, firm, true, firmness) |
| refractory(adjective, strain, firmness, labour, hardiness) |
| resilient(adjective, strain, firmness, labour, hardiness) |