| inexorable(adjective, appearance, mean, strong, hard) |
| unrelenting(adjective, animal, appearance, mean, strong) |
| rigid(adjective, mean, strong, hard, tough) |
| inflexible(adjective, mean, strong, hard, tough) |
| stubborn(adjective, characteristic, appearance, quality, mean) |
| uncompromising(adjective, mean, hard, tough, severe) |
| intransigent(adjective, resist, determined, resolute, obstinate) |
| determined(adjective, strong, hard, tough, firm) |
| obdurate(adjective, mean, strong, hard, tough) |
| unyielding(adjective, appearance, mean, strong, hard) |
| unbending(adjective, mean, strong, hard, tough) |
| resolute(adjective, appearance, strong, tough, severe) |
| firm(adjective, mean, strong, hard, tough) |
| insistent(adjective, determined, resolute, obstinate, uncompromising) |
| stiff(adjective, tough, severe, firm, harsh) |
| immovable(adjective, mean, strong, hard, tough) |
| adamant(adjective, mean, strong, hard, tough) |
| persistent(adjective, strong, tough, severe, continue) |
| adamantine(adjective, strong, hard, tough, resist) |
| set(adjective, determined, resolute, obstinate, unyielding) |