hardness

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The quality or condition of being hard.
• noun The relative resistance of a mineral to scratching, as measured by the Mohs scale.
• noun The relative resistance of a metal or other material to denting, scratching, or bending.

from The Century Dictionary.

• noun Water, as found in nature, containing salts of lime or magnesia or both of these in considerable quantity, is said to be hard; it curdles or precipitates soap bv forming insoluble lime or magnesia salts of the fatty acids. Any lime or magnesia present in the condition of carbonate is held in solution by carbonic acid, and if this latter is driven off as carbon-dioxid gas by boiling the water, the earthy carbonates are precipitated, so that the water is to this extent softened. The part of the original hardness which is thus removable by boiling is called temporary hardness. The part due to calcium or magnesium in the condition of chlorid or sulphate is not thus removable, and is called permanent hardness. The sum of the temporary and permanent hardness constitutes the total hardness. Hardness is frequently stated in degrees, each degree representing hardness equivalent to that caused by 1 grain of calcium carbonate in 1 imperial gallon of water; or, now more commonly, 1 part of calcium carbonate in 1,000,000 parts of water.
• noun The state or quality of being hard, in any of the senses of that word; solidity; density; difficulty of comprehension, accomplishment, control, or endurance; obduracy; harshness; severity; inclemency; adversity; roughness; uncomeliness; want of sensibility.
• noun Specifically That quality in fountain-water which is imparted by the presence in excess of earthy salts, especially calcium sulphate.
• noun In medicine, that quality of the pulse which is due to tension of the artery, which in this condition does not readily yield to the pressure of the finger.
• noun In art and music, harshness or coldness of execution; unsympathetic treatment, as of a tone or the details of a picture; want of feeling in performance.
• noun In mineralogy, the comparative capacity of a substance to scratch another or be scratched by another; the quality of bodies which enables them to resist abrasion of their surfaces.

from the GNU version of the Collaborative International Dictionary of English.

• noun The quality or state of being hard, literally or figuratively.
• noun (Min.) The cohesion of the particles on the surface of a body, determined by its capacity to scratch another, or be itself scratched; -- measured among minerals on a scale of which diamond and talc form the extremes.
• noun (Chem.) The peculiar quality exhibited by water which has mineral salts dissolved in it. Such water forms an insoluble compound with soap, and is hence unfit for washing purposes.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The quality of being hard.
• noun An instance of this quality; hardship.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the property of being rigid and resistant to pressure; not easily scratched; measured on Mohs scale
• noun devoid of passion or feeling; hardheartedness
• noun a quality of water that contains dissolved mineral salts that prevent soap from lathering
• noun the quality of being difficult to do
• noun excessive sternness