noun
Physical or metaphorical hardness; can refer to material properties, consistency, or rigidity. The kanji choice (硬・固・堅) may reflect nuance: 硬 for general hardness, 固 for solidity, 堅 for stiffness/tightness.
このパンは固さがちょうどいい。
This bread has just the right firmness.
金属の硬さを測る。
Measure the hardness of the metal.
noun
honesty; integrity; uprightness
Only when written 堅さ
Metaphorical use referring to a person's character: being principled, honest, or unwavering. Often written 堅さ in this sense.
彼の堅さは誰もが認めるところだ。
Everyone acknowledges his integrity.
Noun form of the adjective 硬い/固い/堅い (hard, firm, stiff), derived by adding the nominalizing suffix さ to the stem.