Hardness

What does HARDNESS mean?

1. noun

   the property of being rigid and resistant to pressure; not easily scratched; measured on Mohs scale

2. noun

   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. noun

   devoid of passion or feeling; hardheartedness

4. noun

   the quality of being difficult to do

   “he assigned a series of problems of increasing hardness”

Definitions from WordNet 3.1, Princeton University.