| bold(adjective, strong, resolute, spirited, brave) |
| insurmountable(adjective, steadfast, unyielding, impossible, insuperable) |
| unmanageable(adjective, difficult, wild, awkward, persistent) |
| indefatigable(adjective, strong, firm, determined, steady) |
| intractable(adjective, difficult, violent, persistent, obstinate) |
| persistent(adjective, strong, firm, determined, steady) |
| unwavering(adjective, strong, firm, determined, steady) |
| recalcitrant(adjective, difficult, violent, wild, awkward) |
| relentless(adjective, strong, hard, tough, determined) |
| stalwart(adjective, strong, powerful, bold, spirited) |
| stoic(adjective, cool, tolerant, unemotional, enduring) |
| unassailable(adjective, strong, secure, resolute, steadfast) |
| unbeatable(adjective, strong, secure, resolute, steadfast) |
| undaunted(adjective, strong, bold, resolute, spirited) |
| plucky(adjective, strong, bold, resolute, spirited) |
| business-minded |
| fractious(adjective, cross, violent, wild, unruly) |
| inflexible(adjective, set, strong, hard, tough) |
| intrepid(adjective, strong, bold, spirited, brave) |
| stiff(adjective, hard, rigid, inflexible, strict) |