An instance of this quality; hardship.
The quality of being hard.
The resistance to scratching, cutting, indentation or abrasion of a metal or other solid material.
The penetrating ability of electromagnetic radiation, such as x-rays; generally, the shorter the wavelength, the harder and more penetrating the radiation.
The measure of resistance to damage of a facility, equipment, installation, or telecommunications infrastructure when subjected to attack.
A measure of how hard a material is
The quantity of calcium carbonate dissolved in water, usually expressed in parts per million (ppm).
The state or quality of being unkind.
An unkind act.
The collective noun for ravens