something or someone that causes trouble; a source of unhappiness; "washing dishes was a nuisance before we got a dish washer"; "a bit of a bother"; "he's not a friend, he's an infliction"
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"
the property of being rigid and resistant to pressure; not easily scratched; measured on Mohs scale