1. The property of being rigid and resistant to pressure; not easily scratched; measured on Mohs scale
   "The hardness of diamond makes it ideal for cutting tools"
    
2. A quality of water that contains dissolved mineral salts that prevent soap from lathering
   "the costs of reducing hardness depend on the relative amounts of calcium and magnesium compounds that are present"
    
3. The quality of being difficult to do
   "he assigned a series of problems of increasing hardness";
   - ruggedness
    
4. Devoid of passion or feeling; hardheartedness
   "The hardness in his voice made her step back";
   - unfeelingness, callousness, callosity, insensibility, cold-bloodedness

See also: hard, soft

Type of: body, consistence, consistency, difficultness, difficulty, insensitiveness, insensitivity, quality, substance

Antonym: softness

Encyclopedia: Hardness