| persistent(adjective, strong, tough, continue, strain) |
| enduring(verb, adjective, calm, strong, great) |
| stable(adjective, strong, tough, strain, firm) |
| permanent(adjective, calm, strong, secure, tough) |
| firm(adjective, calm, strong, secure, tough) |
| strong(adjective, strain, firmness, labour, hardiness) |
| consistent(adjective, strain, certain, fixed, firmness) |
| sound(adjective, strain, firmness, labour, hardiness) |
| constant(adjective, calm, strong, secure, tough) |
| hard(adjective, strain, firmness, labour, hardiness) |
| stiff(adjective, strain, firmness, labour, hardiness) |
| unfluctuating(adjective, calm, strong, secure, strain) |
| durable(adjective, continue, strain, firmness, sturdy) |
| perpetual(adjective, strain, stable, fixed, firmness) |
| fast(adjective, strain, firmness, labour, permanent) |
| steadfast(adjective, calm, strong, secure, strain) |
| long-standing(adjective, continue, strain, firmness, labour) |
| invariable(adjective, calm, strong, secure, strain) |
| lingering(verb, adjective, great, strain, deep) |
| steady(adjective, calm, strong, secure, strain) |