insanity

Etymology

It is borrowed from Latin īnsānitās (“unsoundness, especially of the mind”),^[2][3][4][5] from īnsānus (“mad, insane”) and the noun suffix -tās;^[2][3][4] the adjective is the source of insane, and is formed from in- (“not”) and sānus (“sound, healthy”).^[3][6] In Latin īnsānitās meant unhealthiness or unsoundness, while the usual noun for madness was īnsānia.^[3] The OED compares French insanité, recorded only from 1784.^[2]

Earliest recorded meaning

The condition of being insane: 1590, in Swinburne's treatise on wills and testaments.^[2] Etymonline dates it to the 1580s^[3] and Merriam-Webster to 1650.^[7]

Semantic evolution

The word entered English in a legal treatise, and the law kept a sense of its own: an unsoundness of mind that removes a person's capacity to make a contract or their criminal responsibility, as in not guilty by reason of insanity.^{[2][8][9][10]} The weakened sense of extreme folly or senselessness is recorded from 1651 in the OED,^[2] but only from 1844 in Etymonline.^[3] In medicine the word has become an outmoded term for severe mental illness.^[6][9]

Timeline

• 1590 – the condition of being insane.^[2]
• 1651 – extreme imprudence or senselessness; an instance of this.^[2]

Modern meaning

Noun

1. Severe mental illness; madness.
2. (law) Unsoundness of mind that makes a person unfit to enter into a contract, or not responsible for a crime: She was found not guilty by reason of insanity.
3. Extreme folly or irrationality, or an act that shows it: It would be insanity to drive across the desert without water.

Related words

• insane
• sane
• sanity

Usage notes

The American Heritage Dictionary notes that the word is not used in psychiatric diagnosis,^[9] Stedman's calls it an outmoded term for severe mental illness or psychosis,^[6] and Merriam-Webster labels the medical sense dated.^[7]

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d e f Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
5. ^ Stevenson, Angus, ed. (2010), Oxford Dictionary of English, 3rd ed., Oxford: Oxford University Press
6. ^ a b c Stedman's Medical Dictionary, Baltimore: Lippincott Williams & Wilkins
7. ^ a b Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
8. ^ Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
9. ^ a b c The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
10. ^ Collins English Dictionary (2023), Glasgow: HarperCollins