| firm(noun, adjective, feature, state, characteristic) |
| persistent(adjective, feature, state, characteristic, strain) |
| rigid(adjective, feature, state, characteristic, strong) |
| hard(adjective, feature, state, characteristic, hard) |
| strong(adjective, strong, severe, strain, firm) |
| unyielding(adjective, strong, hard, tough, strain) |
| stable(adjective, secure, strain, firm, steady) |
| sound(adjective, strong, strain, solid, firmness) |
| tight(adjective, close, strong, hard, secure) |
| steadfast(adjective, feature, state, characteristic, strong) |
| inflexible(adjective, hard, tough, severe, rough) |
| steady(adjective, feature, state, characteristic, strain) |
| stubborn(adjective, hard, tough, rough, firm) |
| resistant(adjective, strong, hard, strain, firm) |
| refractory(adjective, hard, tough, strain, rough) |
| durable(adjective, strong, strain, firm, solid) |
| fast(adjective, great, secure, strain, firm) |
| stout(adjective, strong, strain, solid, firmness) |
| substantial(adjective, strain, firmness, labour, hardiness) |
| unalterable(adjective, strain, firmness, labour, hardiness) |