| gruesome(adjective, appearance, terrible, hopeless) |
| hard-line(adjective, strong, hard, tough, firm) |
| hell-bent(adjective, persistent, obstinate, insistent, dogged) |
| inclement |
| indurate(adjective, mean, hard, determined, resolute) |
| inelastic(adjective, determined, resolute, obstinate, uncompromising) |
| intense(adjective, strong, severe, difficult, harsh) |
| invincible(adjective, persistent, obstinate, insistent, dogged) |
| iron-willed(adjective, determined, resolute, uncompromising, unshakeable) |
| mean(adjective, animal, hard, severe, nasty) |
| persisting(adjective, strong, tough, firm, determined) |
| perverse(adjective, mean, hard, tough, determined) |
| puritanical(adjective, severe) |
| recurrent |
| resistant(adjective, determined, resolute, obstinate, uncompromising) |
| rock-ribbed(adjective, determined, resolute, uncompromising, unshakeable) |
| sedulous |
| strong-minded(adjective, determined, resolution, fixed, resolute) |
| thorough(adjective, resolute) |
| true(adjective, strong, tough, firm, determined) |