| tyrannical(adjective, hard, tough, evil, nasty) |
| uncompassionate(adjective, animal, mean, hard, harsh) |
| unconquerable(adjective, persistent, obstinate, insistent, dogged) |
| uncooperative(adjective, mean, hard, persistent, obstinate) |
| undaunted |
| undeviating(adjective, cruel, merciless) |
| unmitigated(adjective, pure, absolute) |
| unregenerate(adjective, hard, tough, harsh, cruel) |
| vehement(adjective, strong, severe, difficult, intense) |
| vindictive(adjective, mean, hard, tough, severe) |
| never-ending(adjective, adverb, determined, constant, obstinate) |
| animal(noun, adjective, mean, strong, severe) |
| ardent(adjective, difficult, intense, resolute, persistent) |
| astringent(adjective, close, strong, hard, tough) |
| authoritarian(adjective, strong, hard, tough, severe) |
| bleak(adjective, appearance, severe, harsh, terrible) |
| bold(adjective, strong, firm, violent, resolute) |
| brutish(adjective, strong, severe, evil, nasty) |
| cantankerous(tough, firm, persistent, obstinate, stubborn) |
| chilly(adjective, severe) |