| rock-hard(adjective, firm, rigid, unyielding, steely) |
| standing pat(adjective, determined, resolute, obstinate, unyielding) |
| staunch(adjective, strong, tough, flat, firm) |
| steady(adjective, strong, secure, flat, firm) |
| steel(adjective, strong, hard, strength, tough) |
| strong-willed(adjective, determined, resolute, uncompromising, unshakeable) |
| unaffected(adjective, cold, indifferent, unyielding) |
| unfeeling(adjective, mean, hard, tough, harsh) |
| unmoving |
| unshakeable(adjective, determined, resolute, uncompromising) |
| apathetic(adjective, person, feelings, emotions) |
| bone(strength, hardness) |
| bovine(adjective, determined, resolute, obstinate, uncompromising) |
| bull-headed(adjective, determined, resolute, obstinate, uncompromising) |
| chilly(adjective, person, feelings, response, emotions) |
| cold(adjective, mean, harsh, indifferent, cruel) |
| contumacious(adjective, tough, firm, determined, unreasonable) |
| cool(adjective, cold, indifferent, unyielding) |
| flint |
| granite(adjective, hardness) |