hardness

1. The quality of being hard.
   • c. 1380s, [Geoffrey Chaucer; William Caxton, editor], The Double Sorow of Troylus to Telle Kyng Pryamus Sone of Troye [...] [Troilus and Criseyde] (in Middle English), [Westminster]: Explicit per Caxton, published 1482, OCLC 863541017 ↗; republished in [William Thynne], editor, The Workes of Geffray Chaucer Newlye Printed, […], book II, [London]: Printed by [Richard Grafton for] Iohn Reynes […], 1542, OCLC 932884868 ↗, folio clxxx, recto ↗:

     For truſteth wel, to longe ydone hardneſſe / Cauſeth diſpyte ful often for diſtreſſe

     For trust this well: Too long maintained hardness / Creates contempt from distress.

   • 1611, The Holy Bible, […] (King James Version), imprinted at London: By Robert Barker, […], OCLC 964384981 ↗, Job 38:37–38 ↗:

     Who can number the cloudes in wiſedom? or who can ſtay the bottles of heauen, / When the duſt groweeh{{sic

2. An instance of this quality; hardship.
3. (inorganic chemistry) The quantity of calcium carbonate dissolved in water, usually expressed in parts per million (ppm).
4. The resistance to scratching, cutting, indentation or abrasion of a metal or other solid material.
5. (physics) The penetrating ability of electromagnetic radiation, such as x-rays; generally, the shorter the wavelength, the harder and more penetrating the radiation.
6. The measure of resistance to damage of a facility, equipment, installation, or telecommunications infrastructure when subjected to attack.

• French: dureté
• German: Härte
• Italian: durezza
• Portuguese: dureza
• Russian: твёрдость
• Spanish: dureza