hardened; hardening
ˈhärd-niŋ 
ˈhär-dᵊn-iŋ
1
: to make hard or harder
2
: to confirm in disposition, feelings, or action
especially
: to make callous
hardened his heart
3
4
: to protect from blast, heat, or radiation (as by a thick barrier or placement underground)
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
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
The confession struck him as both raw and deeply tragic, a glimpse of how ambition hardens into captivity.
—
Eva Roytburg, Fortune, 26 Oct. 2025
Fertilization and pruning encourage new growth, which does not have time to harden off before cold temperatures set in.
—Kim Toscano, Southern Living, 24 Oct. 2025
The finale opens in the stillness that follows, grief hardening into vengeance.
—Jp Mangalindan, Time, 24 Oct. 2025
The ad, purchased by the government of Ontario and broadcast on major US television networks, aired clips of the address, delivered from Camp David, where Reagan was soon to meet the prime minister of Japan at a time when American attitudes toward Japan were hardening.
—David Goldman, CNN Money, 24 Oct. 2025
See All Example Sentences for harden
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show current usage.
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Opinions expressed in the examples do not represent those of Merriam-Webster or its editors.
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Eva Roytburg, Fortune, 26 Oct. 2025
Fertilization and pruning encourage new growth, which does not have time to harden off before cold temperatures set in.
—Kim Toscano, Southern Living, 24 Oct. 2025
The finale opens in the stillness that follows, grief hardening into vengeance.
—Jp Mangalindan, Time, 24 Oct. 2025
The ad, purchased by the government of Ontario and broadcast on major US television networks, aired clips of the address, delivered from Camp David, where Reagan was soon to meet the prime minister of Japan at a time when American attitudes toward Japan were hardening.
—David Goldman, CNN Money, 24 Oct. 2025
See All Example Sentences for harden
Cite this Entry
“Harden.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/harden. Accessed 4 Nov. 2025.
Copy CitationKids 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
noun
ˈhärd-nər
-ᵊn-ər
Biographical Definition
Harden
2 of 2biographical name (2)
Maximilian 1861–1927 originally Felix Ernst Witkowski German writer
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