| inexorable(adjective, tough, severe, firm, harsh) |
| uncompromising(adjective, hard, tough, severe, rough) |
| conservative(adjective, strain, firmness, labour, hardiness) |
| resolute(adjective, strong, hard, tough, severe) |
| robust(adjective, strong, great, strain, solid) |
| unbending(adjective, hard, correct, severe, rough) |
| constant(adjective, strain, firmness, purpose, reliable) |
| resilient(adjective, strong, strain, firmness, tight) |
| enduring(adjective, strain, firmness, labour, hardiness) |
| invariable(adjective, strain, firmness, labour, hardiness) |
| lasting(adjective, strain, firmness, labour, hardiness) |
| proof(adjective, strain, firmness, labour, hardness) |
| quiescent(adjective, strain, firmness, labour, hardiness) |
| rock-solid(adjective, strain, firmness, labour, hardiness) |
| settled(adjective, strain, firmness, labour, hardiness) |
| tenable(adjective, strain, firmness, labour, hardiness) |
| determined(adjective, strong, harsh, solid, cruel) |
| impregnable(adjective, strain, firmness, labour, hardiness) |
| intransigent(adjective, severe, determined, resolute, obstinate) |
| lingering(adjective, strain, firmness, labour, hardiness) |