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[dahy-ur-nl] /daɪˈɜr nl/
of or relating to a day or each day; daily.
of or belonging to the daytime (opposed to nocturnal).
Botany. showing a periodic alteration of condition with day and night, as certain flowers that open by day and close by night.
active by day, as certain birds and insects (opposed to nocturnal).
Liturgy. a service book containing offices for the daily hours of prayer.
Archaic. a diary.
Archaic. a newspaper, especially a daily one.
Origin of diurnal
late Middle English
1400-50; late Middle English < Latin diurnālis, equivalent to diurn(us) daily + -ālis -al1
Related forms
diurnally, adverb
diurnalness, noun
transdiurnal, adjective
undiurnal, adjective
undiurnally, adverb
Can be confused
diurnal, nocturnal. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for diurnal
  • Charles's many books yield an abundance of light/sky imagery, both diurnal and nocturnal.
  • That diurnal migration is something that the research team here hopes to shed some light on.
  • Furthermore, he said, some insects are particularly sensitive to changes in diurnal variations.
  • This interplay is given its diurnal rhythm by environmental influences, social habits and behavior patterns.
  • His own current studies are focussed on the diurnal sleep-wake cycle.
  • That is what other diurnal mammals do.
  • Treat him as you would a baby that you're trying to get on a diurnal schedule.
  • It doesn't even have to be all that cold, but anything that resembles some diurnal fluctuation in temperature is welcome.
  • The gray squirrel is diurnal and has the keen eyesight to match.
  • Dogs are diurnal, so they generally tend to sleep through the night, and mine do.
British Dictionary definitions for diurnal


happening during the day or daily
(of flowers) open during the day and closed at night
(of animals) active during the day Compare nocturnal
a service book containing all the canonical hours except matins
Derived Forms
diurnally, adverb
Word Origin
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
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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
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diurnal in Medicine

diurnal di·ur·nal (dī-ûr'nəl)

  1. Having a 24-hour period or cycle; daily.

  2. Occurring or active during the daytime rather than at night.

di·ur'nal·ly adv.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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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 © 2002. Published by Houghton Mifflin. All rights reserved.
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