What is a synonym for "hardness"?

Common synonyms include: callosity, severity, stiffness, unfeelingness, abstruseness, apathy.

Hardness

//ˈhɑɹdnəs// noun

noun ·Common ·High school level

Noun

1
The quality of being hard. countable, uncountable
"Who can number the cloudes in wiſedom? or who can ſtay the bottles of heauen, / When the duſt groweeh^([sic – meaning groweth]) into hardneſſe and the clods cleaue faſt together?"
2
excessive sternness wordnet
3
An instance of this quality; hardship. countable, uncountable
4
the quality of being difficult to do wordnet
5
The quantity of calcium carbonate dissolved in water, usually expressed in parts per million (ppm). countable, uncountable

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6
devoid of passion or feeling; hardheartedness wordnet
7
The resistance to scratching, cutting, indentation or abrasion of a metal or other solid material. countable, uncountable
8
a quality of water that contains dissolved mineral salts that prevent soap from lathering wordnet
9
The penetrating ability of electromagnetic radiation, such as x-rays; generally, the shorter the wavelength, the harder and more penetrating the radiation. countable, uncountable
10
the property of being rigid and resistant to pressure; not easily scratched; measured on Mohs scale wordnet
11
The measure of resistance to damage of a facility, equipment, installation, or telecommunications infrastructure when subjected to attack. countable, uncountable
12
A measure of how hard a material is. countable
"The hardness of the material was high."