| tough(adjective, strong, hard, firm, harsh) |
| adamantine(adjective, strong, hard, tough, firm) |
| stony(adjective, firm, rigid, stern, unyielding) |
| hard(adjective, strong, tough, severe, evil) |
| unbreakable(adjective, strong, hard, firm, solid) |
| impenetrable(adjective, firm, rigid, unyielding, steely) |
| indestructible(adjective, firm, rigid, unyielding, steely) |
| rock-hard(adjective, firm, rigid, unyielding, steely) |
| cruel(adjective, strong, hard, tough, severe) |
| steely(adjective, strong, hard, tough, firm) |
| unyielding(adjective, strong, hard, tough, severe) |
| rigid(adjective, strong, hard, tough, severe) |
| rocky(adjective, firm, rigid, inflexible, rugged) |
| adamant(adjective, strong, hard, tough, firm) |
| firm(adjective, strong, hard, tough, severe) |
| obdurate(adjective, close, strong, hard, tough) |
| unsympathetic(adjective, severe, harsh, strict, stern) |
| unfeeling(adjective, close, hard, severe, evil) |
| severe(adjective, strong, hard, tough, harsh) |
| harsh(adjective, strong, hard, tough, severe) |