| hanging tough(expression, adjective, mean, hard, determined) |
| hard-boiled(adjective, mean, hard, tough, sharp) |
| hard-core(firm, determined, resolute, impulsive, reckless) |
| hard-hearted(adjective, mean, hard, harsh, inflexible) |
| hard-line(tough, firm, difficult, determined, awkward) |
| immutable(adjective, obstinate, stubborn, unbending) |
| indefatigable |
| indomitable(tough, difficult, determined, awkward, fixed) |
| indurate(adjective, mean, hard, harsh, inflexible) |
| insubordinate(tough, firm, unreasonable, grim, inflexible) |
| intent(adjective, firm, determined, usual, regular) |
| inveterate(adjective, firm, determined, usual, regular) |
| iron(adjective, mean, hard, tough, firm) |
| ironclad(adjective, firm, determined, usual, regular) |
| mean(adjective, hard, harsh, awkward, inflexible) |
| mule(tough, firm, unreasonable, grim, impulsive) |
| mutinous |
| ornery(tough, firm, unreasonable, grim, inflexible) |
| ossified(adjective, determined, resolute, uncompromising, unshakeable) |
| overbearing |