| hard(adjective, mean, strong, tough, severe) |
| steadfast(adjective, strong, secure, tough, flat) |
| insistent(adjective, determined, resolute, obstinate, uncompromising) |
| adamantine(adjective, strong, hard, tough, firm) |
| tough(adjective, mean, strong, hard, severe) |
| implacable(adjective, mean, strong, hard, tough) |
| unbendable(adjective, firm, resist, determined, unreasonable) |
| intractable(adjective, strong, hard, tough, rough) |
| hard-nosed(adjective, mean, strong, hard, secure) |
| severe(adjective, strong, hard, tough, severe) |
| dogged(adjective, mean, strong, hard, tough) |
| mulish(adjective, mean, strong, hard, tough) |
| inelastic(adjective, hard, tough, firm, solid) |
| stern(adjective, hard, tough, severe, rough) |
| strict(adjective, strong, hard, tough, moderate) |
| tenacious(adjective, strong, determined, resolute, obstinate) |
| unwavering(adjective, strong, secure, flat, firm) |
| unchangeable(adjective, strong, secure, moderate, flat) |
| grim(adjective, strong, hard, tough, severe) |
| resolved(adjective, strong, severe, flat, firm) |