| persistent(adjective, feature, state, characteristic, strong) |
| firm(noun, adjective, activity, feature, state) |
| stable(adjective, calm, good, quiet, strong) |
| constant(adjective, calm, good, close, quiet) |
| strong(adjective, calm, good, sound, secure) |
| steadfast(adjective, feature, state, move, characteristic) |
| consistent(adjective, calm, strong, smooth, right) |
| stiff(adjective, feature, state, characteristic, strain) |
| unfluctuating(adjective, calm, strong, secure, smooth) |
| sound(adjective, calm, quiet, strong, secure) |
| hard(adjective, feature, state, characteristic, strain) |
| invariable(adjective, calm, quiet, quality, strong) |
| fast(adjective, adverb, calm, close, strong) |
| regular(adjective, calm, quiet, quality, smooth) |
| settled(adjective, characteristic, strong, secure, easy) |
| durable(adjective, calm, strong, sound, secure) |
| perpetual(adjective, strain, determined, familiar, usual) |
| unwavering(adjective, characteristic, calm, close, strong) |
| permanent(adjective, calm, strong, secure, strain) |
| unyielding(adjective, strong, sound, secure, tough) |