| unyielding(adjective, strain, firmness, labour, hardiness) |
| well-established(adjective, strain, firmness, labour, hardiness) |
| fast(adjective, strain, firmness, labour, hardiness) |
| stabile(adjective, strain, firmness, labour, hardiness) |
| stationary(adjective, strain, firmness, labour, hardiness) |
| stout(adjective, strain, firmness, labour, hardiness) |
| substantial(adjective, strain, firmness, labour, hardiness) |
| sustained(adjective, strain, firmness, labour, hardiness) |
| long-lasting(adjective, continue, existing) |
| long-lived(adjective, continue, persistent, hardened, lasting) |
| abiding(adjective, continue, steady, even, hardened) |
| continuing(adjective, continue, persistent, continuous, hardened) |
| chronic(adjective, persistent, continuous, hardened, lasting) |
| fixed(adjective, complete, true, persistent, customary) |
| perdurable(adjective, continue, steady, even, unchanging) |
| inveterate(adjective, persistent, continuous, hardened, lasting) |
| perennial(adjective, continue, persistent, continuous, hardened) |
| time-consuming |
| traditional(adjective, existing) |
| immutable(steady, even, unchanging) |