| persistent(adjective, quiet, strong, tough, continue) |
| lasting(verb, adjective, calm, strong, great) |
| stable(adjective, strong, sound, tough, strain) |
| permanent(adjective, calm, strong, secure, tough) |
| firm(adjective, calm, close, strong, sound) |
| strong(adjective, strain, powerful, healthy, firmness) |
| sound(adjective, calm, strong, secure, tough) |
| hard(adjective, strain, firmness, labour, hardiness) |
| constant(adjective, calm, close, strong, secure) |
| consistent(adjective, strong, strain, flat, firm) |
| stiff(adjective, strain, firmness, labour, hardiness) |
| unfluctuating(adjective, calm, strong, secure, strain) |
| perpetual(adjective, strain, determined, familiar, steady) |
| durable(adjective, calm, strong, sound, secure) |
| steadfast(adjective, calm, close, strong, complete) |
| abiding(verb, adjective, calm, strong, complete) |
| steady(adjective, calm, close, strong, sound) |
| long-standing(adjective, continue, strain, firmness, labour) |
| staying(verb, adjective, strain, firmness, labour) |
| invariable(adjective, calm, strong, secure, strain) |