| indomitable(adjective, hard, resolute, rigid, inflexible) |
| intractable(adjective, set, tough, firm, distant) |
| iron(adjective, set, hard, stiff, rigid) |
| locked in(expression, adjective, tough, firm, distant) |
| pig-headed(adjective, determined, resolute, obstinate, uncompromising) |
| reserved(adjective, tough, firm, fixed, distant) |
| rigorous(adjective, hard, resolute, rigid, inflexible) |
| single-minded(adjective, set, tough, firm, distant) |
| steely(adjective, set, hard, stiff, rigid) |
| strict(hard, tough, fixed, rigid, reserved) |
| stringent(adjective, set, hard, stiff, rigid) |
| tenacious(adjective, determined, resolute, obstinate, uncompromising) |
| tough(adjective, determined, resolute, obstinate, uncompromising) |
| unadaptable(adjective, set, hard, stiff, rigid) |
| unchangeable(adjective, set, hard, stiff, rigid) |
| unflexible(adjective, tough, firm, fixed, distant) |
| unmovable |
| unpersuadable |
| unpliable |
| unreceptive |