| rigorous(adjective, strong, hard, tough, severe) |
| set in stone(adjective, determined, resolute, obstinate, stubborn) |
| unshakeable(adjective, determined, resolute, uncompromising) |
| unswayable(adjective, determined, resolute, rigid, obstinate) |
| austere(adjective, mean, strong, hard, tough) |
| cold-blooded(adjective, person, mean, hard, cool) |
| hardheaded(adjective, strong, hard, tough, determined) |
| hidebound(adjective, severe, determined, resolute, obstinate) |
| merciless(adjective, person, mean, hard, tough) |
| pat(adjective, difficult, determined, resolute, obstinate) |
| pitiless(adjective, mean, hard, tough, severe) |
| refractory(adjective, tough, firm, difficult, determined) |
| resolved(adjective, strong, determined, definite, resolute) |
| standing pat(adjective, determined, resolute, obstinate, uncompromising) |
| strict(adjective, strong, hard, tough, severe) |
| uncompassionate(adjective, person, mean, hard, cool) |
| unrepentant(adjective, impenitence) |
| wilful(adjective, determined, resolute, uncompromising, unshakeable) |
| cold(adjective, mean, hard, cool, tough) |
| cruel(adjective, mean, strong, hard, cool) |