Hardening p. pr. & vb. n. : of Harden

Hardening n. : Making hard or harder.

Hardening n. : That which hardens, as a material used for converting the surface of iron into steel.

Example:
How do I keep old-fashioned/organic peanut butter from Hardening in the refrigerator?

Taxonomy
hardening, hardening of the arteries, metal, computer, idioms, steel, heat treatment, metal pieces, server, Intelligence, Britannica Concise Encyclopedia, Computer Desktop Encyclopedia, heat, steel surface, substance, chill hardening, Encyclopedia, Translations.

Defination from the web:
hardening n. The act or process of becoming hard or harder. Something that hardens, as a substance added to iron to yield steel ... hardening, in metallurgy, treatment of metals to increase their resistance to penetration. ...