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
sudden expulsion of air from the lungs that clears the air passages; a common symptom of upper respiratory infection or bronchitis or pneumonia or tuberculosis
exhale abruptly, as when one has a chest cold or congestion; "The smoker coughs all day"