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ironclad

American  
[ahy-ern-klad, ahy-ern-klad] / ˈaɪ ərnˈklæd, ˈaɪ ərnˌklæd /

adjective

  1. covered or cased with iron plates, as a ship for naval warfare; armor-plated.

  2. very rigid or exacting; inflexible; unbreakable.

    an ironclad contract.

noun

  1. a wooden warship of the middle or late 19th century having iron or steel armor plating.

ironclad British  

adjective

  1. covered or protected with iron

    an ironclad warship

  2. inflexible; rigid

    an ironclad rule

  3. not able to be assailed or contradicted

    an ironclad argument
"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

noun

  1. a large wooden 19th-century warship with armoured plating

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Etymology

Origin of ironclad

First recorded in 1850–55; iron + clad 1

Explanation

Something ironclad is either covered in iron for protection or protected in a different way. An ironclad guarantee can’t be broken or taken back. Originally, this word was very literal: an ironclad battleship was clad (covered) in iron. Since then, this word is more metaphorical, though it still applies to things you can trust. An ironclad contract is unbreakable. An ironclad promise can be believed wholeheartedly. If you were arrested on ironclad charges, you’re going to be found guilty.

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Vocabulary lists containing ironclad

The American Civil War

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President Trump's First State of The Union Address (2018)

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Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

China has also invested billions into infrastructure projects in Pakistan as part of President Xi Jinping's Belt and Road initiative and the two governments call themselves "ironclad brothers."

From Barron's • Apr. 10, 2026

Nvidia’s next earnings report in November made it clear the $100 billion figure wasn’t exactly an ironclad commitment.

From MarketWatch • Feb. 1, 2026

Its defense agreement fell short of the ironclad mutual-defense pact it wants.

From The Wall Street Journal • Nov. 21, 2025

But if they don’t include ironclad provisions outlawing impoundment under all circumstances, those concessions won’t be worth the paper they’re printed on.

From Slate • Sep. 10, 2025

The routine was ironclad, which put the weight of responsibility on Barack to either make it on time or not.

From "Becoming" by Michelle Obama

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.