Idiom

Mad as a Hatter

Meaning: Completely crazy or very strange in behavior (informal and a little old-fashioned).

In English, saying someone is "mad as a hatter" means they're acting crazy. This phrase originates from the 18th and 19th centuries when hat makers used mercury in their work, leading to mercury poisoning, which caused erratic behavior.​

How to use it

It’s a playful way to describe wild or eccentric behavior. Use it for funny, harmless habits, not about someone’s real mental illness, where it can sound unkind. Many people connect it with the Hatter in “Alice’s Adventures in Wonderland,” often called the Mad Hatter.

Examples

A common mistake

Keep the article: (as) mad as a hatter, not “mad like hatter.” Also, in American English “mad” alone usually means angry, but in this phrase it means crazy.

Where it comes from

The most common explanation: hat makers in the 1700s and 1800s used mercury to make felt, and mercury poisoning caused shaking and strange behavior. That health problem was real, but no one can prove it is where the phrase came from. The phrase was already in use decades before Lewis Carroll’s Hatter appeared in 1865.

Say it out loud

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Source: The Henry Ford

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