| indefatigable(adjective, strong, continue, firm, difficult) |
| unflagging(adjective, strong, continue, firm, difficult) |
| untiring(adjective, strong, continue, energetic, lively) |
| persevering(adjective, strong, firm, difficult, energetic) |
| persistent(adjective, strong, firm, energetic, determined) |
| resolute(adjective, set, strong, firm, energetic) |
| determined(adjective, strong, keen, firm, energetic) |
| industrious(adjective, work, strong, strain, difficult) |
| steadfast(adjective, determined, resolute, tenacious) |
| diligent(adjective, work, strain, firmness, resolute) |
| dogged(adjective, strong, firm, energetic, determined) |
| energetic(adjective, determined, active, vigorous, full) |
| sedulous(adjective, work, strain, active, firmness) |
| active(adjective, strong, difficult, energetic, lively) |
| assiduous(adjective, work, strain, active, firmness) |
| unfailing(adjective, set, strong, continue, firm) |
| unfaltering(adjective, strong, firm, energetic, determined) |
| unwavering(adjective, set, strong, firm, determined) |
| unwearying(adjective, determined) |
| staunch(adjective, strong, firm, determined, steady) |