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 material also had to harden with strength similar to natural bone and gradually break down so new bone could replace it.
—
Bojan Stojkovski, Interesting Engineering, 27 Sep. 2025
Here, the situation has changed, leaving many of the gods either hardened or embittered by the conflict.
—Christopher Cruz, Rolling Stone, 27 Sep. 2025
Harsh chemicals like bleach will damage or harden rubber, so choose the appropriate cleaner based on the material your seal is made from.
—Brandee Gruener, Southern Living, 26 Sep. 2025
The waterless Wadi Hammamat between the Nile and the Red Sea was quarried for the siltstone formed from ancient river sediment that had hardened over millions of years to provide a limitless supply of stone coffins (sarcophagi).
—Vanessa Taylor, Big Think, 25 Sep. 2025
See All Example Sentences for harden
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Bojan Stojkovski, Interesting Engineering, 27 Sep. 2025
Here, the situation has changed, leaving many of the gods either hardened or embittered by the conflict.
—Christopher Cruz, Rolling Stone, 27 Sep. 2025
Harsh chemicals like bleach will damage or harden rubber, so choose the appropriate cleaner based on the material your seal is made from.
—Brandee Gruener, Southern Living, 26 Sep. 2025
The waterless Wadi Hammamat between the Nile and the Red Sea was quarried for the siltstone formed from ancient river sediment that had hardened over millions of years to provide a limitless supply of stone coffins (sarcophagi).
—Vanessa Taylor, Big Think, 25 Sep. 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 Oct. 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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