| perpetual(adjective, strain, firmness, labour, hardiness) |
| resistant(adjective, strain, firmness, sturdy, labour) |
| robust(adjective, strong, sound, secure, tough) |
| tough(verb, adjective, calm, strong, sound) |
| invariable(adjective, strain, stable, firmness, stability) |
| rigid(adjective, strong, strain, firm, stiff) |
| unyielding(adjective, strong, sound, tough, strain) |
| resilient(adjective, strain, firmness, labour, hardiness) |
| unalterable(adjective, strain, firmness, stability, labour) |
| settled(adjective, strong, secure, strain, firm) |
| stationary(adjective, strain, firmness, labour, hardiness) |
| tenable(adjective, strain, firmness, labour, hardiness) |
| quiescent(adjective, strain, firmness, labour, hardiness) |
| refractory(adjective, strain, firmness, labour, hardiness) |
| rock-solid(adjective, strain, firmness, labour, hardiness) |
| stabile(adjective, calm, strong, secure, strain) |
| staying(adjective, strain, firmness, labour, hardiness) |
| sustained(adjective, strain, firmness, labour, hardiness) |
| tight(adjective, strain, firmness, labour, hardiness) |
| abundant(adjective, strain, firmness, labour, hardiness) |