| inexorable(adjective, appearance, mean, strong, hard) |
| inflexible(adjective, mean, strong, hard, tough) |
| relentless(adjective, animal, appearance, mean, strong) |
| stubborn(adjective, characteristic, appearance, quality, mean) |
| intransigent(adjective, tough, resist, determined, resolute) |
| uncompromising(adjective, mean, hard, tough, severe) |
| unyielding(adjective, appearance, mean, strong, hard) |
| rigid(adjective, mean, strong, hard, tough) |
| obdurate(adjective, mean, strong, hard, tough) |
| unbending(adjective, mean, strong, hard, tough) |
| determined(adjective, severe, harsh, cruel, fierce) |
| resolute(adjective, firm, determined, rigid, obstinate) |
| firm(noun, adjective, mean, strong, hard) |
| immovable(adjective, mean, strong, hard, tough) |
| adamant(adjective, mean, strong, hard, tough) |
| adamantine(adjective, strong, hard, tough, resist) |
| insistent(adjective, determined, resolute, obstinate, demanding) |
| stiff(adjective, tough, severe, firm, harsh) |
| implacable(adjective, animal, appearance, mean, strong) |
| grim(adjective, animal, appearance, mean, strong) |