hallucination

Etymology

It is borrowed from Latin hallūcinātiō (“a wandering of the mind”),^[2][3][4] a later form of ālūcinātiō,^[5][6][7] which the OED classes as Late Latin.^[8] It is a noun of action from ālūcinor (“to wander in mind, talk idly, prate”).^[8][5][6] The verb is generally traced to Ancient Greek ἀλύω (alúō, “to be distraught, be beside oneself”),^{[5][9][4][10]} an origin that Barnhart and Etymonline give as probable,^[7][6] and which they and Klein connect with ἀλάομαι (aláomai, “to wander, roam”).^[7][6][4] The ending was probably influenced by vāticinor (“to prophesy; to rave”).^[4][6][5] The OED compares French hallucination, which it finds in the dictionary of the French Academy in 1835.^[8]

Earliest recorded meaning

The apparent perception of an external object that is not actually there: 1646, in Sir Thomas Browne's Pseudodoxia Epidemica.^[8][7] Merriam-Webster dates this sense earlier, to 1629.^[11] Etymonline and Dictionary.com give the 1640s,^[6][2] and the Shorter Oxford and Word Origins the early 17th century.^[3][9]

Semantic evolution

The Latin verb was about wandering in mind or talk rather than about the senses,^[8][4] and English used the noun for both things in the same decades.^[8] Beside Browne's perception of what is not there, it meant from before 1652, in John Smith's Select Discourses, the state of being deceived or a belief with nothing real behind it.^[8][3] Johnson (1755) knew only this looser use, defining it as "errour; blunder; mistake; folly", and quoted Addison on a "hallucination of the transcriber".^[12] The related verb hallucinate had started out meaning "to deceive", in 1604.^[8][7] The medical and psychological sense is now the main one: Stedman's lists hallucinations of every sense, visual, auditory, olfactory, gustatory and tactile,^[13] and Dictionary.com links them with disorders and toxic substances.^[2] The newest sense comes from computing: first recorded in 1995 in a Usenet post, it meant a novel or unexpected output from a machine-learning program, and is now usually applied to the responses of generative programs.^[8]

Timeline

• 1646 – an apparent perception of something not present, in Browne.^[8][7] Merriam-Webster dates the sense to 1629.^[11]
• before 1652 – the condition of being mistaken; an unfounded belief, in John Smith.^[8]
• 1995 – a novel or unexpected output from a machine-learning program.^[8]

Meanings

Noun

1. An apparent perception of something with no external cause, usually seen or heard, as a result of a disorder or a drug: The fever gave him vivid hallucinations of insects on the ceiling.^{[14][11][2][13]}
2. The thing or scene perceived in this way.^[11][2]
3. A mistaken idea with no basis in fact; a delusion.^[11][8][3]
4. In artificial intelligence, an unexpected output from a machine-learning program, now usually a response from a generative program.^[8]

Word family

• hallucinational
• nonhallucination
• hallucinative
• hallucinatory

Related words

• hallucinate
• hallucinogen

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
3. ^ a b c d Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
4. ^ a b c d e Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
5. ^ a b c d Hoad, T. F., ed. (1986), The Concise Oxford Dictionary of English Etymology, Oxford: Clarendon Press
6. ^ a b c d e f Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
7. ^ a b c d e f Barnhart, Robert K., ed. (1995), The Barnhart Concise Dictionary of Etymology, New York: HarperCollins
8. ^ a b c d e f g h i j k l m n Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
9. ^ a b Cresswell, Julia (2021), Oxford Dictionary of Word Origins, 3rd ed., Oxford: Oxford University Press
10. ^ Beekes, Robert S. P. (2010), Etymological Dictionary of Greek, with the assistance of Lucien van Beek, Leiden Indo-European Etymological Dictionary Series 10, Leiden; Boston: Brill
11. ^ a b c d e Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
12. ^ Johnson, Samuel (1755), A Dictionary of the English Language, London; 4th ed. 1773; Johnson's Dictionary Online, ed. Beth Rapp Young et al.
13. ^ a b Stedman's Medical Dictionary, Baltimore: Lippincott Williams & Wilkins
14. ^ Collins English Dictionary (2023), Glasgow: HarperCollins