| persistent(adjective, tough, strain, flat, firm) |
| firm(noun, adjective, calm, good, set) |
| sound(noun, adjective, calm, clear, strong) |
| hard(adjective, person, body, tough, strain) |
| stable(adjective, good, strong, hard, sound) |
| stiff(adjective, severe, strain, firm, thin) |
| robust(adjective, person, clear, body, hard) |
| unfluctuating(adjective, strain, firmness, labour, hardiness) |
| mighty(adjective, feature, characteristic, good, person) |
| consistent(adjective, strain, firmness, labour, hardiness) |
| substantial(adjective, calm, good, strong, hard) |
| stout(adjective, calm, person, body, great) |
| durable(adjective, calm, sound, secure, tough) |
| powerful(adjective, good, person, clear, body) |
| enduring(adjective, strain, powerful, healthy, firmness) |
| steady(adjective, calm, good, sound, secure) |
| steadfast(adjective, calm, good, tough, easy) |
| vigorous(adjective, person, great, sound, tough) |
| heavy(adjective, feature, characteristic, person, body) |
| formidable(adjective, feature, characteristic, force, power) |