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.

Definitions of ironclad

adj inflexibly entrenched and unchangeable

“an ironclad rule”
incapable of change

adj sheathed in iron plates for protection

enclosed in a protective covering; sometimes used in combination

n a wooden warship of the 19th century that is plated with iron or steel armor

Type of:
combat ship, war vessel, warship
a government ship that is available for waging war

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