noun, noun which may take the genitive case particle 'no'
Technical term used in materials science, engineering, and related fields to describe the property of being hard. Often used attributively with の.
This material has high hardness.
Hard plastics are prone to cracking.
Compound of 硬 (こう, 'hard') and 性 (せい, 'property, nature'). A Sino-Japanese technical term.