| immutable(adjective, calm, strong, hard, secure) |
| steady(adjective, calm, strong, secure, strain) |
| durable(adjective, strain, firmness, stability, labour) |
| fast(adjective, strain, firmness, labour, hardiness) |
| long-standing(adjective, strain, firmness, labour, hardiness) |
| perpetual(adjective, strain, steady, stable, regular) |
| refractory(adjective, hard, strain, rough, harsh) |
| stabile(adjective, calm, strong, secure, strain) |
| stationary(adjective, strain, firmness, labour, hardiness) |
| stout(adjective, strain, firmness, labour, hardiness) |
| substantial(adjective, strain, firmness, labour, hardiness) |
| sustained(adjective, strain, firmness, persistent, continuous) |
| well-balanced(adjective, strain, firmness, even, labour) |
| unchanging(adjective, severe, firm, harsh, solid) |
| changeless |
| inflexible(adjective, set, strong, hard, secure) |
| inalterable(adjective, inflexible, changeable, flexible) |
| irrevocable(adjective, change, set, fixed, necessary) |
| irreversible(adjective, change, complete, fixed, even) |
| certain(adjective, definite, fixed, distinct, rigid) |