| enured |
| habitual(adjective, usual, established) |
| impenitent(adjective, hard, tough, harsh, careless) |
| impervious(noun, adjective, set, hard, tough) |
| indurated(verb, adjective, hard, cool, firm) |
| reinforced(verb, adjective, fortified, strengthened) |
| seasoned(adjective, set, strong, hard, tough) |
| unrelenting(adjective, hard, tough, harsh, determined) |
| unresponsive(adjective, person, hard, careless, indifferent) |
| unyielding(adjective, set, hard, tough, firm) |
| calloused |
| congealed(verb, adjective, set, hard, tough) |
| cool(adjective, indifferent, blank, sophisticated, aloof) |
| dull(noun, physical insensibility) |
| fortified(verb, adjective, strengthened) |
| hard-nosed(adjective, hard, determined, resolute, unfeeling) |
| intransigent(adjective, determined, fixed, resolute, stubborn) |
| obstinate(adjective, determined, fixed, resolute, stubborn) |
| ossified(adjective, firm, solid, determined, resolute) |
| remorseless(adjective, hard, cold, cruel, pitiless) |