Open English Wordnet
Nouns
(n)unfeelingness, callousness, callosity, hardness, insensibilitydevoid of passion or feeling; hardheartedness
(n)hardness, ruggednessthe 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”
(n)severity, severeness, harshness, rigor, rigour, rigorousness, rigourousness, inclemency, hardness, stiffnessexcessive sternness“severity of character”, “the harshness of his punishment was inhuman”, “the rigors of boot camp”