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
a constitutional tendency to be gloomy and depressed
characterized by or causing or expressing sadness; "growing more melancholy every hour"; "her melancholic smile"; "we acquainted him with the melancholy truth"