| persistent(adjective, strong, tough, strain, flat) |
| firm(noun, adjective, state, calm, good) |
| strong(adjective, good, strong, hard, sound) |
| sound(noun, adjective, strong, hard, complete) |
| consistent(adjective, calm, strong, direct, smooth) |
| hard(adjective, strong, strain, firm, solid) |
| unfluctuating(adjective, calm, strong, direct, secure) |
| stiff(adjective, secure, strain, firm, steady) |
| steady(adjective, state, calm, good, quiet) |
| permanent(adjective, quality, strong, secure, tough) |
| constant(adjective, calm, good, quality, strong) |
| steadfast(adjective, calm, good, strong, secure) |
| fast(adjective, adverb, strong, secure, tough) |
| invariable(adjective, state, quiet, soft, gentle) |
| lasting(adjective, quality, strong, tough, strain) |
| durable(adjective, strong, sound, secure, tough) |
| stout(adjective, strong, sound, tough, strain) |
| substantial(adjective, strong, hard, sound, complete) |
| enduring(adjective, quality, strong, sound, tough) |
| stationary(adjective, calm, quiet, strong, secure) |