| formality(firmness, severity, strictness, rigidity, inflexibility) |
| formidability(noun, difficulty) |
| hardiness(noun, strength, resistance, toughness, durability) |
| heart of stone(expression, idiom, malevolence) |
| impenetrability(noun, protection, security, cruelty, rigidity) |
| impermeability(noun, protection, security, rigidity, density) |
| imperviousness(noun, protection, security, rigidity, density) |
| impliability(noun, protection, security, rigidity, density) |
| indifference(noun, insensitivity) |
| inexorability |
| inexorableness |
| inhumanity(noun, malevolence) |
| security(noun, support, control, change, strength) |
| solidness(noun, support, control, strength, balance) |
| stableness(noun, support, control, change, strength) |
| stamina(noun, open-mindedness, lenience, broad-mindedness) |
| steadfastness(noun, support, control, strength, balance) |
| stringiness |
| thickness(firmness, density, texture, impermeability, runniness) |
| ticklishness(noun, difficulty) |