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

Her resilience, shaped by a complex past that’s hardened her resolve, anchors her when the community’s secrets begin to surface. —Borys Kit, The Hollywood Reporter, 30 Oct. 2024

But over the course of its third term, the party made a U-turn and hardened its stance on rapprochement with the West. —Democrat-Gazette Staff From Wire Reports, arkansasonline.com, 27 Oct. 2024

After hardening off, plant the mum outdoors after the last frost in spring, or place the pot in a full sun location and begin fertilizing regularly. —Andy Wilcox, Better Homes & Gardens, 25 Oct. 2024

Apple has now hardened Safari to prevent modification of those configurations files. —Zak Doffman, Forbes, 20 Oct. 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