| persistent(adjective, strong, strain, flat, firm) |
| firm(adjective, set, strong, secure, easy) |
| stable(adjective, strong, secure, easy, strain) |
| unfluctuating(adjective, strong, secure, strain, firm) |
| hard(adjective, strain, firmness, labour, hardiness) |
| sound(adjective, strong, secure, easy, strain) |
| stiff(adjective, strain, firmness, labour, hardiness) |
| strong(adjective, secure, easy, strain, flat) |
| fixed(verb, adjective, set, strong, secure) |
| permanent(adjective, strain, firmness, labour, hardiness) |
| stationary(adjective, strain, firmness, labour, hardiness) |
| steady(adjective, strong, secure, easy, strain) |
| fast(adjective, strong, secure, strain, firm) |
| constant(adjective, strong, strain, flat, firm) |
| steadfast(adjective, strong, secure, easy, strain) |
| stabilized(verb, adjective, strain, firmness, labour) |
| enduring(adjective, strong, strain, flat, firm) |
| lasting(adjective, strain, firmness, labour, hardiness) |
| unalterable(adjective, strain, firmness, labour, hardiness) |
| rigid(adjective, secure, strain, determined, usual) |