| inexorable(adjective, appearance, mean, strong, hard) |
| relentless(adjective, animal, appearance, mean, strong) |
| unrelenting(adjective, animal, appearance, mean, strong) |
| inflexible(adjective, mean, strong, hard, tough) |
| unyielding(adjective, appearance, mean, strong, hard) |
| remorseless(adjective, animal, mean, tough, severe) |
| stubborn(adjective, characteristic, appearance, quality, mean) |
| uncompromising(adjective, mean, hard, harsh, resist) |
| grim(adjective, animal, appearance, mean, strong) |
| intransigent(adjective, tough, resist, determined, resolute) |
| unbending(adjective, mean, strong, hard, tough) |
| obdurate(adjective, mean, strong, hard, tough) |
| rigid(adjective, mean, strong, hard, tough) |
| ruthless(adjective, animal, appearance, mean, hard) |
| adamantine(adjective, strong, hard, tough, resist) |
| adamant(adjective, mean, strong, hard, tough) |
| stern(adjective, appearance, mean, harsh, terrible) |
| unforgiving(adjective, mean, hard, tough, severe) |
| merciless(adjective, appearance, mean, hard, tough) |
| intractable(adjective, hard, tough, firm, cruel) |