| strong(verb, adjective, calm, sound, secure) |
| persistent(adjective, continue, strain, stable, firmness) |
| stable(adjective, strong, sound, secure, tough) |
| firm(noun, adjective, calm, strong, sound) |
| sound(adjective, calm, strong, secure, tough) |
| hard(adjective, strong, strain, firm, stiff) |
| lasting(adjective, continue, strain, firmness, sturdy) |
| stiff(adjective, strong, strain, firm, solid) |
| consistent(adjective, strain, stable, firmness, labour) |
| permanent(adjective, continue, strain, stable, firmness) |
| substantial(adjective, calm, strong, sound, secure) |
| unfluctuating(adjective, calm, strong, secure, strain) |
| enduring(adjective, calm, strong, sound, secure) |
| stout(adjective, calm, strong, sound, secure) |
| constant(adjective, calm, strong, secure, tough) |
| fast(adjective, calm, strong, secure, tough) |
| steady(adjective, calm, strong, sound, secure) |
| sturdy(adjective, calm, strong, sound, secure) |
| long-standing(adjective, continue, strain, firmness, labour) |
| steadfast(adjective, calm, strong, secure, strain) |