the state or quality of being hard

the hardness of ice.

a relative degree or extent of this quality

wood of a desirable hardness.

that quality in water that is imparted by the presence of dissolved salts, esp. calcium sulfate or bicarbonate.

unfeelingness or jadedness; callousness.

harshness or austerity, as of a difficult existence.

South Midland U.S. ill will; bad feelings

There's a lot of hardness between those two boys.

Mineralogy . the comparative ability of a substance to scratch or be scratched by another. Compare Mohs scale .

Metallurgy . the measured resistance of a metal to indention, abrasion, deformation, or machining.

noun

fastness , firmness , security , soundness , stableness , steadiness , strength , sturdiness , sureness , austerity , harshness , rigidity , rigor , rigorousness , sternness , strictness , stringency , toughness