What does 'As mad as a hatter' mean?
Meaning: This simile means that someone is crazy or behaves very strangely. In the past many people who made hats went insane because they had a lot of contact with mercury.
Buy our lists of British English, American English and Animal idioms in PDF format. They're perfect to use offline for reference or for use in class!
If you have a question about idioms, ask us about it in our Idioms Discussion Forum.
If you know of an idiom that you would like to be listed here, please use our online form to suggest an idiom.