1. the state or quality of being hard: the hardness of ice.
  2. a relative degree or extent of this quality: wood of a desirable hardness.
  3. that quality in water that is imparted by the presence of dissolved salts, especially calcium sulfate or bicarbonate.
  4. unfeelingness or jadedness; callousness.
  5. harshness or austerity, as of a difficult existence.
  6. South Midland U.S. ill will; bad feelings: There’s a lot of hardness between those two boys.
  7. Mineralogy. the comparative ability of a substance to scratch or be scratched by another.Compare Mohs scale.
  8. Metallurgy. the measured resistance of a metal to indention, abrasion, deformation, or machining.


  1. the quality or condition of being hard
  2. one of several measures of resistance to indentation, deformation, or abrasionSee Mohs scale, Brinell hardness number
  3. the quality of water that causes it to impair the lathering of soap: caused by the presence of certain calcium salts. Temporary hardness can be removed by boiling whereas permanent hardness cannot

Old English heardnysse; see hard + -ness. Meaning “difficulty of action or accomplishment” is late 14c.

  1. A measure of how easily a mineral can be scratched. Hardness is measured on the Mohs scale.
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