| imperceptive(adjective, hard, indifferent, unkind, unresponsive) |
| indurate(adjective, mean, hard, tough, harsh) |
| inured(noun, adjective, hard, careless, indifferent) |
| merciless(adjective, hard, tough, severe, cruel) |
| pitiless(adjective, hard, tough, severe, cruel) |
| reserved(adjective, calm, cool, indifferent, restrained) |
| ruthless(adjective, hard, tough, severe, cruel) |
| steeled(noun, adjective, hard, unfeeling, unsympathetic) |
| steely |
| tough-skinned |
| unaffected(adjective, calm, hard, cool, careless) |
| addictive |
| aloof(adjective, calm, hard, indifferent, restrained) |
| asleep(adjective, hard, tough, severe, cruel) |
| chilly(adjective, indifferent, detached, distant, remote) |
| cold fish(expression, adjective, calm, mean, hard) |
| constitutionally |
| deadened(adjective, hard, tough, severe, cruel) |
| flawed |
| flexible |