| opinionated(adjective, tough, firm, determined, unreasonable) |
| pigheaded(adjective, tough, firm, determined, unreasonable) |
| plodding(adjective, strong, firm, determined, steady) |
| prolonged(adjective, continue, constant, lasting, protracted) |
| reliable(adjective, strong, tough, honest, certain) |
| remaining(adjective, current, enduring, lasting, ongoing) |
| serious(adjective, strong, firm, determined, bold) |
| stern(adjective, resolute, obstinate, insistent, dogged) |
| sticky(adjective, informal, determined) |
| sturdy |
| timeless(adjective, continue, steady, constant, continuous) |
| undying(adjective, continuous) |
| unfading(stable, constant, enduring, lasting, permanent) |
| unshakeable(adjective, resolute) |
| unstoppable |
| unwearied(adjective, strong, firm, energetic, determined) |
| zealous(adjective, resolute) |
| around-the-clock(adjective, continue, continual) |
| bloody-minded(adjective, obstinate, insistent, dogged) |
| careful |