| sturdy(adjective, strong, hard, tough, rugged) |
| unapologetic |
| unshakeable(adjective, determined, resolute, uncompromising) |
| unswerving(adjective, determined, resolute, uncompromising, unshakeable) |
| unwavering(adjective, determined, resolute, uncompromising, unshakeable) |
| cold-hearted(adjective, cold, unfeeling, unsympathetic, pitiless) |
| concrete |
| constant(adjective, resolute) |
| dark |
| dense(adjective, strong, hard, tough, sturdy) |
| dogged(adjective, set, hard, stiff, resolute) |
| fixed(adjective, hard, firm, solid, rigid) |
| forbidding(adjective, strong, hard, tough, severe) |
| grey(adjective, dull, leaden) |
| harsh(adjective, strong, hard, tough, severe) |
| heartless(adjective, cold, cruel, unfeeling, unsympathetic) |
| hearty(adjective, resolute) |
| immutable(adjective, set, hard, stiff, rigid) |
| impervious |
| incompliant(adjective, firm, solid, determined, resolute) |