hardener

UK: /ˈhɑːd^ənə/ US: (här′dn ər)

WordReference Random House Unabridged Dictionary of American English © 2025

hard•en•er  (här′dn ər), n. 

1. a person or thing that hardens.
2. a substance mixed with paint or other protective covering to make the finish harder or more durable.
3. Photography a chemical used to raise the melting point of an emulsion.

• harden + -er¹ 1605–15

Collins Concise English Dictionary © HarperCollins Publishers::

hardener / ˈhɑːd^ənə/ noun

1. a person or thing that hardens
2. a substance added to paint or varnish to increase durability
3. an ingredient of certain adhesives and synthetic resins that accelerates or promotes setting

WordReference Random House Learner's Dictionary of American English © 2025

hard•en /ˈhɑrdən/   v. 

1. to (cause to) become hard or harder: [no object]
   The ice cream hardened in the freezer.
   [~ + object]
   The freezer will harden the ice cream.
2. to (cause to) become pitiless, unfeeling, or less gentle and sympathetic: [no object]
   His heart hardened with anger.
   [~ + object]
   His cruel life had hardened his heart.
3. to cause to become stronger;
   toughen:
   [~ + object] Battle had hardened the troops.

hard•en•er, n. [countable]

WordReference Random House Unabridged Dictionary of American English © 2025

hard•en  (här′dn), v.t. 

1. to make hard or harder:
   to harden steel.
2. to make pitiless or unfeeling:
   to harden one's heart.
3. to make rigid or unyielding;
   stiffen:
   The rigors of poverty hardened his personality.
4. to strengthen or confirm, esp. with reference to character, intentions, feelings, etc.;
   reinforce.
5. to make hardy, robust, or capable of endurance;
   toughen.
6. Military to reinforce the structure of (a military or strategic installation) to protect it from nuclear bombardment.

v.i. 

7. to become hard or harder.
8. to become pitiless or unfeeling.
9. to become rigid or unyielding;
   stiffen:
   His personality hardened over the years.
10. to become confirmed or strengthened:
    His resistance hardened.
11. to become inured or toughened:
    The troops hardened under constant fire.
12. Business [Com.] (of a market, prices, etc.)
    • to cease to fluctuate;
      firm:
      When the speculators withdrew from the market, the prices hardened.
    • to rise higher.

• 1150–1200; Middle English; see hard, -en¹

hard′en•a•ble, adj. 
hard′en•a•bil′i•ty, n. 
Synonyms

• 1. . solidify, indurate; petrify, ossify.
• 4. . fortify, steel, brace, nerve.

Antonyms

• 1. . soften.
• 4. . weaken.

Har•den  (här′dn), n. 

1. Biographical Sir Arthur, 1865–1940, English biochemist: Nobel prize 1929.