| intractable(adjective, set, hard, stiff, rigid) |
| level(adjective, certain, limited, definite, inflexible) |
| obdurate(adjective, strong, hard, definite, inflexible) |
| regular(adjective, set, firm, solid, stable) |
| reliable(adjective, calm, strong, secure, firm) |
| rigorous(adjective, hard, resolute, rigid, inflexible) |
| steely(adjective, set, hard, stiff, resolute) |
| stern(adjective, resolute, rigid) |
| unchanged(adjective, fixed, static, unvarying, unalterable) |
| unflinching(adjective, strong, flat, certain, determined) |
| unqualified(adjective, strong, flat, firm, solid) |
| unshakable(adjective, clear, strong, certain, steady) |
| bold(adjective, resolute) |
| certain(adjective, clear, firm, solid, determined) |
| continuous(adjective, continuous) |
| decisive(adjective, resolute) |
| determinate(adjective, certain, limited, definite, inflexible) |
| everlasting(adjective, continuous, permanent) |
| formal |
| homogeneous(adjective, continuous) |