See more synonyms for diurnal on Thesaurus.com
  1. of or relating to a day or each day; daily.
  2. of or belonging to the daytime (opposed to nocturnal).
  3. Botany. showing a periodic alteration of condition with day and night, as certain flowers that open by day and close by night.
  4. active by day, as certain birds and insects (opposed to nocturnal).
  1. Liturgy. a service book containing offices for the daily hours of prayer.
  2. Archaic. a diary.
  3. Archaic. a newspaper, especially a daily one.

Origin of diurnal

1400–50; late Middle English < Latin diurnālis, equivalent to diurn(us) daily + -ālis -al1
Related formsdi·ur·nal·ly, adverbdi·ur·nal·ness, nountrans·di·ur·nal, adjectiveun·di·ur·nal, adjectiveun·di·ur·nal·ly, adverb
Can be confuseddiurnal nocturnal
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for diurnal

Historical Examples of diurnal

British Dictionary definitions for diurnal


  1. happening during the day or daily
  2. (of flowers) open during the day and closed at night
  3. (of animals) active during the dayCompare nocturnal
  1. a service book containing all the canonical hours except matins
Derived Formsdiurnally, adverb

Word Origin for diurnal

C15: from Late Latin diurnālis, from Latin diurnus, from diēs day
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 diurnal

late 14c., from Late Latin diurnalis "daily," from Latin dies "day" + -urnus, an adjectival suffix denoting time (cf. hibernus "wintery"). Dies "day" is from PIE root *dyeu- "to shine" (cf. Sanskrit diva "by day," Welsh diw, Breton deiz "day;" Armenian tiw; Lithuanian diena; Old Church Slavonic dini, Polish dzień, Russian den), literally "to shine" (cf. Greek delos "clear;" Latin deus, Sanskrit deva "god," literally "shining one;" Avestan dava- "spirit, demon;" Lithuanian devas, Old Norse tivar "gods;" Old English Tig, genitive Tiwes, see Tuesday).

Online Etymology Dictionary, © 2010 Douglas Harper

diurnal in Medicine


  1. Having a 24-hour period or cycle; daily.
  2. Occurring or active during the daytime rather than at night.
Related formsdi•urnal•ly adv.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

diurnal in Science


    1. Occurring once in a 24-hour period; daily.
    2. Having a 24-hour cycle. The movement of stars and other celestial objects across the sky are diurnal.
  1. Most active during the daytime. Many animals, including the apes, are diurnal.
  2. Having leaves or flowers that open in daylight and close at night. The morning glory and crocus are diurnal. Compare nocturnal.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.