| mortal(adjective, mean, severe, harsh, cruel) |
| resolved(adjective, determined, resolute, rigid, uncompromising) |
| rigorous(adjective, strong, hard, tough, severe) |
| strict(adjective, strong, hard, tough, severe) |
| unflinching(adjective, mean, severe, harsh, cruel) |
| unmoved(adjective, pitiless, intolerant) |
| unsympathetic(adjective, animal, mean, hard, tough) |
| bullheaded(adjective, strong, hard, tough, firm) |
| indurate(adjective, mean, hard, determined, resolute) |
| permanent(adjective, persistent, constant, continuous, endless) |
| perverse(adjective, mean, hard, tough, harsh) |
| rock-ribbed(adjective, determined, resolute, uncompromising, unshakeable) |
| stony(adjective, mean, hard, harsh, cruel) |
| unbroken(adjective, violent, vicious, fierce, persistent) |
| unceasing(adjective, persistent, constant, continuous, endless) |
| unfaltering(adjective, perseverance) |
| uninterrupted(adjective, persistent, constant, continuous, endless) |
| willful(adjective, determined, resolute, uncompromising, unshakeable) |
| barbarous(adjective, animal, appearance, mean, hard) |
| bitter(adjective, strong, hard, tough, severe) |