Definition of mad hatter in English:

mad hatter

noun

  • A highly eccentric or crazy character (frequently in "mad hatter's tea party").

Origin

Early 20th century; earliest use found in The Westminster Gazette. After the name of the eccentric host at the ‘mad tea-party’ in Lewis Carroll's Alice's Adventures in Wonderland; in this, and in the phrase mad as a hatter, the allusion is to the effects of mercury poisoning sometimes formerly suffered by hat-makers as a result of the use of mercurous nitrate in the manufacture of felt hats.