definition of
hardness

[1] #1 hardness n. the property of being rigid and resistant to pressure; not easily scratched; measured on Mohs scale. wn

[2] #2 hardness n. a quality of water that contains dissolved mineral salts that prevent soap from lathering; "the costs of reducing hardness depend on the relative amounts of calcium and magnesium compounds that are present". wn

[3] #3 hardness n. [unfeelingness, callousness, callosity, insensibility] devoid of passion or feeling; hardheartedness. wn

[4] #4 hardness n. [ruggedness] the quality of being difficult to do; "he assigned a series of problems of increasing hardness"; "the ruggedness of his exams caused half the class to fail". wn

[5] #5 hardness n. [severity, severeness, harshness, rigor, rigour, rigorousness, rigourousness, inclemency, stiffness] excessive sternness; "severity of character"; "the harshness of his punishment was inhuman"; "the rigors of boot camp". wn