harden

¹ American  

[hahr-dn] / ˈhɑr dn /

verb (used with object)

1. to make hard or harder.

   to harden steel.

   Synonyms:

   ossify, petrify, indurate, solidify

   Antonyms:

   soften

2. to make pitiless or unfeeling.

   to harden one's heart.

3. to make rigid or unyielding; stiffen.

   The rigors of poverty hardened his personality.

4. to strengthen or confirm, especially with reference to character, intentions, feelings, etc.; reinforce.

   Synonyms:

   nerve, brace, steel, fortify

   Antonyms:

   weaken

5. to make hardy, robust, or capable of endurance; toughen.

6. Military. to reinforce the structure of (a military or strategic installation) to protect it from nuclear bombardment.

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verb (used without object)

1. to become hard or harder.

2. to become pitiless or unfeeling.

3. to become rigid or unyielding; stiffen.

   His personality hardened over the years.

4. to become confirmed or strengthened.

   His resistance hardened.

5. to become inured or toughened.

   The troops hardened under constant fire.

6. Commerce. (of a market, prices, etc.)

   1. to cease to fluctuate; firm.

      When the speculators withdrew from the market, the prices hardened.

   2. to rise higher.

Harden ² American  

[hahr-dn] / ˈhɑr dn /

noun

1. Sir Arthur, 1865–1940, English biochemist: Nobel Prize 1929.

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harden ¹ British  

/ ˈhɑːdən /

verb

1. to make or become hard or harder; freeze, stiffen, or set

2. to make or become more hardy, tough, or unfeeling

3. to make or become stronger or firmer

   they hardened defences

4. to make or become more resolute or set

   hardened in his resolve

5. (intr) commerce

   1. (of prices, a market, etc) to cease to fluctuate

   2. (of price) to rise higher

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harden ² British  

/ ˈhɑːdən /

noun

1. a rough fabric made from hards

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Other Word Forms

• hardenability noun
• hardenable adjective
• overharden verb
• preharden verb (used with object)
• reharden verb
• unharden verb (used with object)
• unhardenable adjective

Etymology

Origin of harden

Middle English word dating back to 1150–1200; hard, -en ¹

Example Sentences

The grid has also been repeatedly battered by storms and fires, requiring rebuilding and investment to harden equipment against future damage.

From The Wall Street Journal • Apr. 14, 2026

The service takes technical measures to harden the security of its server network.

From Salon • Mar. 13, 2026

Here is his list of 11 stocks to harden your portfolio against Iran risk.

From MarketWatch • Mar. 13, 2026

Done right, market-structure legislation could harden the financial perimeter that underpins sanctions and law enforcement.

From Barron's • Feb. 5, 2026

They’re not my brothers, Annabeth argued, which made her stepmother’s expression harden.

From "The Mark of Athena" by Rick Riordan