To accustom by labor or suffering to endure with constancy; to strengthen; to stiffen; to inure; also, to confirm in wickedness or shame; to make unimpressionable.
To cause a change in the crystal structure of steel that increases its wear resistance and toughness. This is commonly done through quenching the steel when it has reached a specific temperature, the criticial temperature.
Harden is a small lunar impact crater that lies in the eastern part of the interior floor of the Mendeleev walled-plain. It is located on the far side of the Moon, and can not been seen from the Earth except by spacecraft.