| indefatigable(adjective, strong, tough, continue, fit) |
| tireless(adjective, strong, continue, firm, difficult) |
| untiring(adjective, strong, continue, firm, solid) |
| persistent(adjective, strong, firm, certain, determined) |
| unfaltering(adjective, strong, firm, solid, energetic) |
| unwavering(adjective, set, strong, firm, solid) |
| persevering(adjective, strong, firm, difficult, energetic) |
| steadfast(adjective, perseverance, persevering, tenacious) |
| unfailing(adjective, strong, continue, firm, certain) |
| dogged(adjective, strong, firm, solid, energetic) |
| resolute(adjective, strong, firm, solid, determined) |
| determined(adjective, strong, firm, solid, steady) |
| constant(adjective, strong, firm, certain, determined) |
| staunch(adjective, strong, tough, fit, firm) |
| steady(adjective, strong, complete, firm, total) |
| stubborn(adjective, tenacious) |
| tenacious(adjective, strong, tough, fit, firm) |
| unrelenting(adjective, persistent, continuous, perseverance) |
| unswerving(adjective, set, strong, complete, firm) |
| unwearying |