mad as a hatter

Completely mad (poss from the odd behaviour of some hatters due to mental and physical disorders caused by the mercury in the chemicals used in the making of felt hats)

my hat!

An exclamation of surprise or disbelief

pass or send round the hat

To take up a collection, solicit contributions

take off one's hat to

1. To acknowledge in admiration (figurative)
2. To praise

talk through one's hat

To talk wildly or nonsensically

throw one's hat into the ring see under ring¹

under one's hat

In confidence

wear several hats, another hat, etc

To act in several capacities, another capacity, etc

mad /mad/

adjective (maddˈer; maddˈest)

1. Mentally disordered or deranged
2. Insane
3. Resulting from or caused by madness
4. Extremely and recklessly foolish
5. (often with about or for) extremely enthusiastic
6. Infatuated
7. Violently affected by pain, strong emotion, appetite, etc
8. Furious with anger (informal; orig US)
9. Extravagantly playful or exuberant
10. Rabid

transitive verb (Shakespeare)

To drive mad

intransitive verb (archaic)

1. To be mad
2. To act madly or irrationally

maddˈen transitive verb

1. To make mad
2. To enrage

intransitive verb

1. To go mad
2. To act as if mad

maddˈening adjective

1. Driving to madness
2. Making very angry
3. Extremely annoying

maddˈeningly adverb

maddˈing adjective (archaic)

Distracted, acting madly

maddˈingly adverb (archaic)

madˈling noun (archaic)

A mad person

madˈly adverb

1. Insanely, irrationally
2. Frantically
3. Extremely (informal)

madˈness noun

madˈbrain or madˈbrained adjective (Shakespeare)

1. Mentally disordered
2. Rash
3. Hot-headed

madˈ-bred adjective (Shakespeare)

Bred in madness or heat of passion

madˈcap noun

1. A person who acts madly
2. A wild, rash, or hot-headed person
3. An exuberantly playful person

adjective

Fond of wild and reckless or extravagantly playful behaviour

mad cow disease noun

Bovine spongiform encephalopathy (see under bovine)

madˈ-doctor noun (obsolete)

A person who studied and treated mental illness

Mad Hatter noun

A character in Lewis Carroll's Alice in Wonderland given to irrational behaviour and logic-chopping (see also hatter under hat)

madˈhouse noun

1. A place characterized by noise, confusion, and unpredictable behaviour
2. A mental hospital (obsolete)

madˈman or madˈwoman noun

1. A man or woman who is insane
2. A foolish and reckless man or woman

madˈwort noun

A plant believed to cure canine madness (Alyssum, Asperugo, etc)

go mad

1. To go insane
2. To become very angry (informal)

like mad

With great speed or energy, furiously

mad as a hatter see under hat