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  1. the quality of being easily understood, completely intelligible, or comprehensible: She makes her argument with pointed logic and exemplary lucidity.
  2. the ability to see things clearly; rationality; sanity: In a rare moment of lucidity, the senator sided with his political enemies for the good of the country.
Sometimes lu·cid·ness.
Related formsnon·lu·cid·i·ty, noun


  1. easily understood; completely intelligible or comprehensible: a lucid explanation.
  2. characterized by clear perception or understanding; rational or sane: a lucid moment in his madness.
  3. shining or bright.
  4. clear; pellucid; transparent.

Origin of lucid

1575–85; < Latin lūcidus, equivalent to lūc-, stem of lūx light1 + -idus -id4
Related formslu·cid·i·ty, lu·cid·ness, nounlu·cid·ly, adverbnon·lu·cid, adjectivenon·lu·cid·ly, adverbnon·lu·cid·ness, nounun·lu·cid, adjectiveun·lu·cid·ly, adverbun·lu·cid·ness, noun

Synonyms for lucid

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Antonyms for lucid

1, 4. obscure. 2. irrational. 3. dim. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for lucidness


  1. readily understood; clear
  2. shining or glowing
  3. psychiatry of or relating to a period of normality between periods of insane or irresponsible behaviour
Derived Formslucidity or lucidness, nounlucidly, adverb

Word Origin for lucid

C16: from Latin lūcidus full of light, from lūx light
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for lucidness



1590s, "bright, shining," from Latin lucidus "light, bright, clear," figuratively "perspicuous, lucid, clear," from lucere "to shine," from lux (genitive lucis) "light," from PIE root *leuk- "to shine, be bright" (see light (n.)). Sense of "easy to understand" first recorded 1786. Lucid interval "period of calm or temporary sanity" (1580s) is from Medieval Latin lucida intervalla (plural), which was common in medieval English legal documents (cf. non est compos mentis, sed gaudet lucidis intervallis). Related: Lucidly; lucidness (1640s).



1650s, "brightness," from French lucidité, from Late Latin luciditas, from lucidus (see lucid). Meaning "intellectual clarity" attested by 1851.

Online Etymology Dictionary, © 2010 Douglas Harper

lucidness in Medicine


  1. Clarity, especially mental clarity.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.