| dense(adjective, set, strong, hard, tough) |
| hard-core(adjective, strong, hard, tough, firm) |
| hard-line(adjective, strong, hard, tough, severe) |
| impenetrable(adjective, set, hard, tough, firm) |
| impervious(adjective, hard, tough, solid, rigid) |
| indefatigable(adjective, resolute) |
| invincible(adjective, indestructible) |
| iron-willed(adjective, determined, resolute, uncompromising, unshakeable) |
| loyal(adjective, strong, firm, determined, bold) |
| resisting(adjective, unwilling, resistant, undefeated) |
| rock-ribbed(adjective, determined, resolute, uncompromising, unshakeable) |
| rugged(adjective, strong, hard, sound, tough) |
| standing pat(adjective, determined, resolute, obstinate, uncompromising) |
| strong-minded(adjective, firm, determined, fixed, resolute) |
| true(adjective, strong, tough, flat, firm) |
| uncooperative(adjective, mean, hard, tough, harsh) |
| all-conquering |
| bold(adjective, resolute) |
| concrete(adjective, set, hard, tough, firm) |
| courageous(adjective, resolute) |