harden

Harden is a verb meaning to make something hard or to become harder. It is used to describe physical processes that increase a material’s resistance to deformation, impact, or wear, as well as more abstract forms of resilience or fortification.

The word comes from the English adjective hard, with the derivational suffix -en, indicating the making or becoming of that quality.

In materials science and engineering, hardening refers to methods that increase a metal’s hardness. Common approaches include work hardening (increasing dislocations through plastic deformation), heat treatment (quenching followed by tempering to balance hardness and toughness), case hardening or carburizing to build a hard surface layer, nitriding, and induction or surface hardening. Hardness is measured with standard tests such as Brinell, Rockwell, or Vickers, and higher hardness often trades off with reduced ductility.

Beyond metals, the term is used in information technology and biology. System hardening involves configuring software, services, and networks to reduce vulnerabilities and an attack surface. In botany, hardening off is the gradual acclimatization of indoor-grown plants to outdoor conditions before transplanting. In civil engineering and disaster planning, hardening describes strengthening infrastructure and applying durable surfaces to improve resilience.

In everyday language, to harden one’s resolve means to become more steadfast or determined. The term thus spans technical contexts of physical material properties and broader applications relating to security, growth, and resilience.