noun
hardness
HAHD-nuhs
noun
1
The quality of being physically hard or resistant to scratching, cutting, or denting.
"Diamond has the highest hardness of any natural material."
"Engineers test the hardness of the alloy before using it."
2
The amount of dissolved minerals, especially calcium, in water.
"The hardness of the tap water left limescale on the kettle."
How to Use Hardness
Learner’s notesIn plain EnglishHow hard something is — used for materials (like metal) as well as for mineral content in water.
Common pairings
water hardness
hardness scale
degree of hardness
Word Forms
hardnesses plural
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Diamond has the highest _____ of any natural material.
Etymology
From Old English heardnes, built from hard + the suffix -ness.