| persistent(adjective, continue, strain, firmness, labour) |
| stable(adjective, strain, firmness, labour, hardiness) |
| strong(adjective, strain, firmness, labour, hardiness) |
| firm(adjective, strain, firmness, labour, hardiness) |
| consistent(adjective, strain, firmness, labour, hardiness) |
| sound(adjective, strain, firmness, labour, hardiness) |
| unfluctuating(adjective, strain, firmness, labour, hardiness) |
| lasting(adjective, continue, strain, firmness, labour) |
| enduring(adjective, continue, strain, firmness, labour) |
| durable(adjective, continue, strain, firmness, labour) |
| permanent(adjective, continue, strain, firmness, labour) |
| steady(adjective, strain, firmness, labour, hardiness) |
| steadfast(adjective, strain, firmness, labour, hardiness) |
| constant(adjective, strain, firmness, labour, hardiness) |
| invariable(adjective, strain, firmness, labour, hardiness) |
| lingering(adjective, strain, firmness, labour, hardiness) |
| perpetual(adjective, strain, firmness, labour, hardiness) |
| settled(adjective, strain, firmness, labour, hardiness) |
| staying(adjective, strain, firmness, labour, hardiness) |
| unalterable(adjective, strain, firmness, labour, hardiness) |