From WordNet (r) 2.0 (August 2003) [wn]:
hardness
n 1: the property of being rigid and resistant to pressure; not
easily scratched; measured on Mohs scale [ant:
softness]
2: devoid of passion or feeling [syn: unfeelingness,
callousness, insensibility]
3: the quality of being difficult to do; "he assigned a series
of problems of increasing hardness"
4: excessive sternness; "severity of character"; "the harshness
of his punishment was inhuman"; "the rigors of boot camp"
[syn: severity, harshness, rigor, rigour,
inclemency, stiffness]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Hardness \Hard"ness\, n. [AS. heardness.]
1. The quality or state of being hard, literally or
figuratively.
[1913 Webster]
The habit of authority also had given his manners
some peremptory hardness. --Sir W.
Scott.
[1913 Webster]
2. (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.
[1913 Webster]
3. (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.
[1913 Webster]
Note: This quality is caused by the presence of calcium
carbonate, causing temporary hardness which can be
removed by boiling, or by calcium sulphate, causing
permanent hardness which can not be so removed, but may
be improved by the addition of sodium carbonate.
[1913 Webster]