| fixed(adjective, mean, hard, firm, determined) |
| unshakable(adjective, mean, strong, hard, tough) |
| harsh(adjective, mean, strong, hard, tough) |
| implacable(adjective, animal, appearance, mean, strong) |
| obstinate(adjective, mean, strong, hard, tough) |
| grim(adjective, animal, appearance, mean, strong) |
| steadfast(adjective, strong, tough, firm, determined) |
| cruel(adjective, appearance, mean, strong, hard) |
| remorseless(adjective, animal, mean, tough, severe) |
| stern(adjective, appearance, mean, severe, harsh) |
| ruthless(adjective, animal, appearance, mean, hard) |
| unforgiving(adjective, mean, hard, tough, severe) |
| unremitting(adjective, adverb, hard, tough, continue) |
| unbendable(adjective, resist, determined, resolute, persistent) |
| tenacious(adjective, strong, tough, firm, determined) |
| constant(adjective, continue, firm, determined, steady) |
| severe(adjective, appearance, mean, strong, hard) |
| dogged(adjective, appearance, mean, strong, hard) |
| hard-nosed(adjective, mean, strong, hard, tough) |
| merciless(adjective, appearance, mean, hard, tough) |