mad as a hatter

idiomatic phrase

informal + old-fashioned
: severely mentally unsound
"Mad as a hatter," said the housekeeper. "Talks to himself, runs about waving his arms, won't come in for meals."Eva Ibbotson
"The whole thing is dashed fishy and mysterious and the sooner I can get Mildred safely out of the place, the better I shall be pleased. The fellow's as mad as a hatter!"P. G. Wodehouse

Word History

First Known Use

1827, in the meaning defined above

Time Traveler
The first known use of mad as a hatter was in 1827

Dictionary Entries Near mad as a hatter

Cite this Entry

“Mad as a hatter.” Dictionary, Merriam-Webster, Accessed 29 Nov. 2023.

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