- the state or quality of being hard (in various senses)
- the relative capacity of a substance for scratching another or for being scratched or indented by another
See hardness in American Heritage Dictionary 4
- The quality or condition of being hard.
- The relative resistance of a mineral to scratching, as measured by the Mohs scale.
- The relative resistance of a metal or other material to denting, scratching, or bending.
Learn more about hardness