simple past tense and past participle of harden

Inured; toughened. / Unfeeling; pitiless; callous. / Firmly established or unlikely to change; inveterate. / (computing, military) Having extra defences against attack; highly fortified.

present participle of harden

The process by which something hardens. / That which hardens, such as a material used for converting the surface of iron into steel.

Third-person singular simple present indicative form of harden

(intransitive) To become hard (tough, resistant to pressure). / (transitive, ergative) To make something hard or harder (tough, resistant to pressure). / (transitive, figuratively) To strengthen.

Alternative form of hurden (“coarse linen”)

One who, or that which, hardens. / A chemical substance added to something in order to harden it; used especially with paints, varnishes and resins.

plural of hardener

Capable of being hardened.