hardness

Etymology

From Middle English hardness, hardnesse, from Old English heardness, from heard + -ness. Equivalent to hard + -ness.

noun

1. The quality of being hard.
2. An instance of this quality; hardship.
3. (inorganic chemistry) The quantity of calcium carbonate dissolved in water, usually expressed in parts per million (ppm).
4. The resistance to scratching, cutting, indentation or abrasion of a metal or other solid material.
5. (physics) The penetrating ability of electromagnetic radiation, such as x-rays; generally, the shorter the wavelength, the harder and more penetrating the radiation.
6. The measure of resistance to damage of a facility, equipment, installation, or telecommunications infrastructure when subjected to attack.
7. (countable, engineering) A measure of how hard a material is
   The hardness of the material was high.