the act of leaving secretly or without explanation
the event of passing out of sight
ceasing to exist; "he regretted the disappearance of Greek from school curricula"; "what was responsible for the disappearance of the rainforest?"; "the disappearance of resistance at very low temperatures"
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