delusional

Etymology

It is formed from English delusion + -al.^[2][3] Delusion is from Latin dēlūsiō (“a deceiving”), from dēlūdō (“to delude”), the source of delude.^[3][4]

Earliest recorded meaning

Of the nature of delusion, or affected by delusions: 1858 according to Etymonline,^[2] 1871, in J. R. Reynolds's System of Medicine, in the OED.^[3]

Semantic evolution

The OED's first record is from a medical work, and the adjective draws on the sense of delusion as a fixed false belief, a form of mental disorder, which Etymonline dates to the 1550s.^[3][2] It is now used both of a belief and of a person who holds such beliefs.^[5][6]

Timeline

• 1858 – pertaining to delusion; affected by delusions (Etymonline).^[2]
• 1871 – of the nature of delusion (the OED's first record).^[3]

Meanings

Adjective

1. Having delusions; holding false beliefs that resist evidence: He was delusional about his chances of winning.^[5][6][2]
2. Based on or of the nature of a delusion: a delusional fear of being watched.^[5][3][6]

Related words

• delusion
• delude
• illusion
• allusion
• ludicrous

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
3. ^ a b c d e f Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
4. ^ The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
5. ^ a b c Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
6. ^ a b c Random House Webster's Unabridged Dictionary (1999), 2nd ed., New York: Random House