lucid

Etymology

It is borrowed from Latin lūcidus (“light, bright, clear”),^{[2][3][4][5][6]} perhaps through French lucide or Italian lucido;^[7][8][9] Barnhart takes it both through Middle French and directly from Latin.^[10] The Latin adjective is from lūceō (“to shine”), from lūx (“light”), with the suffix -idus,^[3][6][8] from Proto-Indo-European *leuk- (“to shine, be bright”).^[3][4] It is related to light, lucent, elucidate and pellucid.^[11][10] The phrase lucid interval follows Medieval Latin lūcida intervalla, a plural common in medieval works on lunacy and in legal documents.^[3][12]

Earliest recorded meaning

In lucid interval, a period of calm in the midst of confusion: 1581, in W. Allen's defence of the two English colleges.^[2] On its own the adjective first meant "bright, shining", in Spenser's Prosopopoia (Mother Hubberds Tale, 1591).^{[2][10][5][3]}

Semantic evolution

The literal sense "bright, shining" is now poetic or technical:^[2][8] in entomology and botany lucid means smooth and shining, and in astronomy a lucid star is one visible to the naked eye.^[2][8] Johnson (1755) gave "shining; bright; glittering" first, with a quotation from Milton.^[13] From 1620 the word also meant "translucent, clear".^[2] A lucid interval was, from 1603, a spell of sanity in a person with a mental illness.^[2] From 1656 it was also an interval of sunshine in a storm, which the OED calls the etymological sense;^[2] Etymonline thinks the image was probably that of a calm, clear spell during a storm.^[3] The modern sense "clearly reasoned or expressed, easy to understand" is recorded from 1786,^[2][10][3] and the use of people, "clear-headed, sane", from 1843, in Carlyle.^[2] The noun lucidity followed the same path, from "brightness" in 1656 to intellectual clearness in 1851.^[10]

Timeline

• 1581 – lucid interval, a period of calm amid confusion.^[2]
• 1591 – bright, shining.^[2][10][5]
• 1603 – lucid interval, a period of sanity in a mental illness.^[2]
• 1620 – translucent, clear.^[2]
• 1640s – lucidness.^[3]
• 1656 – lucidity, brightness.^[10]
• 1786 – clear in reasoning or expression, easily understood.^[2][10][3]
• 1843 – of people, clear-headed, sane.^[2]

Meanings

Adjective

1. Clearly expressed and easy to understand: a lucid account of the treaty.^{[14][5][4][2]}
2. Able to think clearly; rational or sane, especially between periods of confusion: The patient was lucid for a few hours each morning.^{[4][5][14][2]}
3. (poetic) Bright, shining, luminous.^{[4][14][2][8]}
4. Clear, translucent.^[4][2][8]
5. (astronomy) Of a star, visible to the naked eye.^[2][8]
6. (entomology, botany) Smooth and shining.^[2][8]

Word family

• lucidity
• lucidly
• lucidness
• nonlucid
• unlucid

Related words

• elucidate
• light
• lucent
• pellucid

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i j k l m n o p q r s t u v Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d e f g h i Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b c d e f The American Heritage Dictionary of the English Language (online 2024), 5th ed., Boston: Houghton Mifflin Harcourt
5. ^ a b c d e Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
6. ^ a b Dictionary.com Unabridged (2016), based on the Random House Unabridged Dictionary, New York: Random House
7. ^ Stevenson, Angus, ed. (2010), Oxford Dictionary of English, 3rd ed., Oxford: Oxford University Press
8. ^ a b c d e f g h Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
9. ^ Hoad, T. F., ed. (1986), The Concise Oxford Dictionary of English Etymology, Oxford: Clarendon Press
10. ^ a b c d e f g h Barnhart, Robert K. (1988), The Barnhart Dictionary of Etymology
11. ^ Klein, Ernest. A Comprehensive Etymological Dictionary of the English Language. 2 vols. Amsterdam: Elsevier, 1966–1967.
12. ^ Weekley, Ernest (1921), An Etymological Dictionary of Modern English, London: John Murray
13. ^ Johnson, Samuel (1755), A Dictionary of the English Language, London; 4th ed. 1773; Johnson's Dictionary Online, ed. Beth Rapp Young et al.
14. ^ a b c Collins English Dictionary (2023), Glasgow: HarperCollins