| remorseless(adjective, mean, tough, harsh, resist) |
| resolved(adjective, strong, flat, firm, certain) |
| self-willed(adjective, tough, firm, determined, resolute) |
| single-minded(adjective, tough, harsh, cruel, determined) |
| unchangeable(adjective, strong, secure, flat, certain) |
| uncompliant(adjective, tough, firm, resist, determined) |
| unswayable(adjective, hard, determined, resolute, obstinate) |
| wilful(adjective, determined, resolute, uncompromising, unshakeable) |
| callous(adjective, person, mean, hard, rough) |
| hardheaded(adjective, strong, hard, tough, determined) |
| impenetrable(adjective, firm, rigid, unyielding, steely) |
| inelastic(adjective, determined, resolute, obstinate, uncompromising) |
| persevering(adjective, strong, tough, flat, firm) |
| rocky(adjective, firm, difficult, rigid, troubled) |
| set in stone(expression, adjective, idiom, mean, hard) |
| brassbound(adjective, resist, determined, resolute, persistent) |
| bullheaded(adjective, strong, hard, tough, firm) |
| die-hard(adjective, resist, determined, resolute, persistent) |
| immutable(adjective, hard, firm, fixed, inflexible) |
| incompliant(adjective, resist, determined, resolute, persistent) |