harden

verb

hard·​en ˈhär-dᵊn 

hardened; hardening ˈhärd-niŋ 

ˈhär-dᵊn-iŋ

transitive verb

1

: to make hard or harder

2

: to confirm in disposition, feelings, or action

especially : to make callous

hardened his heart

3

a

: inure, toughen

harden troops

b

: to inure to unfavorable environmental conditions (such as cold)

—often used with off

harden off seedlings before transplanting

4

: to protect from blast, heat, or radiation (as by a thick barrier or placement underground)

intransitive verb

1

: to become hard or harder

2

a

: to become firm, stable, or settled

b

: to assume an appearance of harshness or severity

her face hardened at the thought

3

: to become gradually acclimatized to unfavorable conditions

—often used with off

plants hardened off before the first frost

Synonyms

• concrete
• congeal
• firm (up)
• freeze
• indurate
• set
• solidify

Examples of harden in a Sentence

The presence of certain substances in the blood can cause the arteries to harden.

These additives are designed to harden the steel.

substances that can harden the arteries

The news has hardened opposition to the government.

He had been hardened by his years of military service.

Recent Examples on the Web

Casualties or not, the specter of future Iranian drone and missile barrages will harden Israel’s desire to degrade or eliminate the threat posed by Iran, its proxies, and its nuclear program. —Suzanne Maloney, Foreign Affairs, 18 Apr. 2024

The group’s negotiating position on a cease-fire deal has only hardened in recent months. —Ahmed Fouad Alkhatib, The Atlantic, 10 Apr. 2024

The British government has been a staunch ally of Israel since the eruption of hostilities on Oct. 7 but Foreign Secretary David Cameron has hardened his language in recent months over the humanitarian situation in Gaza. —NBC News, 5 Apr. 2024

Lin’s determination to secure the rights only hardened after a years-long collaboration with the couple to make a film adaptation fell by the wayside. —Nectar Gan, CNN, 3 Apr. 2024

The commissioner’s mandate was that consumers wouldn’t have to pay for home hardening certification and would be credited for each individual mitigation. —John Woolfolk, The Mercury News, 1 Apr. 2024

Covid-19 was indeed a supply chain crisis, but the system has hardened since then. —Kevin O'Marah, Forbes, 27 Mar. 2024

After the smoke cleared, Mr. Harland found creeks running black with soot and the ground hardening more with every day that passed. —Lydia Depillis, New York Times, 4 Apr. 2024

China’s efforts harden its financial system against climate risk and meet a real investor need. —Edmund Downie, Fortune, 25 Mar. 2024

Word History

First Known Use

13th century, in the meaning defined at transitive sense 1

Phrases Containing harden

• case-harden
• harden one's heart

Kids Definition

harden

verb

hard·​en ˈhärd-ᵊn 

hardened; hardening ˈhärd-niŋ 

-ᵊn-iŋ

1

: to make or become hard or harder

2

: to make unfeeling or unsympathetic

hardened his heart

3

: to make or become hardy or strong

muscles hardened by exercise

4

: to protect from blast, heat, or radiation (as by a thick barrier or by placing underground)

hardened missile sites

5

a

: to become firm, stable, or settled

b

: to express harshness

hardener

ˈhärd-nər

-ᵊn-ər

noun

Biographical Definition

Harden 1 of 2

biographical name (1)

Har·​den ˈhär-dᵊn 

Sir Arthur 1865–1940 English chemist

Harden

2 of 2

biographical name (2)

Maximilian 1861–1927 originally Felix Ernst Witkowski German writer