Meaning of the word "(as) mad as a hatter" in English

What does "(as) mad as a hatter" mean in English? Explore the meaning, pronunciation, and specific usage of this word with Lingoland.

(as) mad as a hatter

US /əz mæd əz ə ˈhætər/
UK /əz mæd əz ə ˈhætər/
"(as) mad as a hatter" picture

Idiom

1.

completely crazy or insane

Example:
My uncle has always been (as) mad as a hatter, always coming up with the wildest ideas.
After working non-stop for three days, he was (as) mad as a hatter.
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