| unapologetic |
| unchangeable(adjective, hard, resolute, rigid, inflexible) |
| unmoved(adjective, cold, cruel, determined, fixed) |
| unpitying(adjective, mean, severe, harsh, cruel) |
| untiring |
| zealous(adjective, difficult, resolute, strenuous, stressful) |
| nonstop(adjective, adverb, direct, continue, persistent) |
| serious(adjective, close, strong, hard, tough) |
| around-the-clock(adjective, continue, continual) |
| assiduous |
| barbarous(adjective, animal, appearance, mean, strong) |
| cold-blooded(adjective, mean, hard, evil, nasty) |
| continuing(adjective, endless, unrelenting, continual, perpetual) |
| cussed(adjective, tough, severe, firm, unreasonable) |
| decisive(adjective, resolute) |
| devoted(adjective, resolute) |
| earnest(adjective, resolute) |
| energetic |
| forbidding(adjective, appearance, strong, hard, tough) |
| grisly(adjective, appearance, terrible, hopeless) |