Definition

1. Adjective:
   • Afflicted with or characteristic of mental derangement; not sane; mentally ill. This describes a person whose mind is severely disordered, making them unable to think or behave rationally.
   • Very foolish; senseless; irrational. This describes an idea, action, or plan that is extremely unwise, impractical, or lacking in common sense.

Usage Examples

• Describing a person's mental state:
  • After the traumatic event, he was declared insane by the court.
  • The insane laughter coming from the empty room was terrifying.
• Describing an idea or action as foolish:
  • Driving that fast in the rain is insane.
  • It was an insane plan with no chance of success.

Advanced Usage

• Legally insane: A legal term for a state of mental illness that negates criminal responsibility.
  • The defense argued the defendant was legally insane at the time of the crime.
• Insanely (adverb): Used for emphasis, meaning "extremely" or "to a foolish degree."
  • The movie was insanely popular. (extremely)
  • He is insanely jealous of his brother's success. (irrationally)

Variants and Related Words

• Insanity (noun): The state of being insane; severe mental illness.
  • The crime was an act of pure insanity.
• Insaneness (noun): A less common synonym for insanity.
• Sane (adjective): The direct opposite, meaning of sound mind; rational.

Synonyms

• Mentally ill, deranged, psychotic (for the medical/legal sense).
• Crazy, mad, foolish, ludicrous, preposterous (for the foolish sense).

Related Phrases

• Insane asylum (historical): An outdated term for a psychiatric hospital.
• Drive someone insane: To irritate or frustrate someone intensely.
  • The constant noise is driving me insane.
• Insane in the membrane (slang/informal): A humorous, exaggerated way to say someone is acting crazy or eccentric, popularized by the song "Insane in the Brain" by Cypress Hill.

Idioms

• Like crazy / like insane: With great intensity, energy, or speed.
  • We had to work like insane to meet the deadline.
• A fine line between genius and insanity: An idiom suggesting that brilliant, innovative ideas can sometimes seem very close to madness.

Adjective

1. very foolish
   • harebrained ideas
   • took insane risks behind the wheel
   • a completely mad scheme to build a bridge between two mountains
2. afflicted with or characteristic of mental derangement
   • was declared insane
   • insane laughter