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

Because of our industry-leading reputation for security, I was invited to serve on a working committee for the Under Secretary of Defense focused solely on hardening the Department of Defense supply chain against terrorism. —Ronald J. Hansen, The Arizona Republic, 12 July 2024

Witnessing a demographic so easily stereotyped as hardened lose themselves within a theatrical setting, even in brief snippets, carries plain emotional weight. —Vikram Murthi, IndieWire, 11 July 2024

Atherosclerosis occurs when a person's arteries harden due to a plaque buildup, per Cleveland Clinic. —Edward Segarra, USA TODAY, 10 July 2024

Soon afterward, as Castro’s rule hardened into a repressive dictatorship, formal relations between the two countries came to an end, and the United States and other countries imposed an economic blockade. —Matt Schudel, Washington Post, 7 July 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