# hardness

> English word · Noun · IPA /ˈhɑɹdnəs/ · frequency rank #23,292

## Definitions
1. The quality of being hard.
2. An instance of this quality; hardship.
3. 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. 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.
7. A measure of how hard a material is.

## Etymology
From Middle English hardness, hardnesse, from Old English heardnes, from heard + -nes, equivalent to hard + -ness.

## Easily confused with
- **harness** (https://plainspell.com/en/vs/hardness-vs-harness)
- **harmless** (https://plainspell.com/en/vs/hardness-vs-harmless)
- **Harkness** (https://plainspell.com/en/vs/hardness-vs-harkness)
- **harshness** (https://plainspell.com/en/vs/hardness-vs-harshness)
- **hardest** (https://plainspell.com/en/vs/hardest-vs-hardness)

## Common misspellings (11)
`ahrdness`, `hadrness`, `harddness`, `hardenss`, `hardnes`, `hardnness`, `hardnses`, `harndess`, `harrdness`, `hhardness`, `hradness`

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/hardness