di·​ur·​nal | \dī-ˈər-nᵊl \

Definition of diurnal 

(Entry 1 of 2)

1a : recurring every day diurnal tasks

b : having a daily cycle diurnal tides

2a : of, relating to, or occurring in the daytime the city's diurnal noises

b biology : active chiefly in the daytime diurnal animals

c botany : opening during the day and closing at night diurnal flowers



Definition of diurnal (Entry 2 of 2)

1 archaic : diary, daybook

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Other Words from diurnal


diurnally \ -​nᵊl-​ē \ adverb

Synonyms for diurnal

Synonyms: Adjective

daily, day-to-day, quotidian

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Examples of diurnal in a Sentence


a love as constant and certain as the diurnal tides


a microfilm containing a collection of diurnals published by 19th-century American abolitionists

Recent Examples on the Web: Adjective

By analyzing coyote scat, scientists have linked this behavioral change to dietary shifts from diurnal to nocturnal prey, with implications for small mammal communities and for competition with other predators. Kaitlyn Gaynor, CNN, "To avoid humans, more wildlife now work the night shift," 14 June 2018 That leaves her beachside club almost the entire day to entertain the diurnal, even if that’s the only trait some of her patrons have in common. New York Times, "You Can’t Hurt Lindsay Lohan Now," 26 June 2018 Sun bears, for example, are typically diurnal and sun-loving creatures; in undisturbed areas less than 20% of their activity occurred at night. Kaitlyn Gaynor, CNN, "To avoid humans, more wildlife now work the night shift," 14 June 2018 That’s the conclusion of a new study, which shows that a variety of previously diurnal animals such as foxes, deer, and boars have become nocturnal to avoid human activity out of fear. Elizabeth Gamillo, Science | AAAS, "Human activity is causing more and more animals to embrace the night," 14 June 2018 Circadian lighting aims to keep the body’s internal clock aligned with the 24-hour diurnal/nocturnal cycle by emitting bright bluish light during the day to suppress the melatonin that our brains produce as a natural sleep aid. New York Times, "These Lights Are Like a Mood Ring for Your Room," 8 May 2018 Eighty mile-per-hour winds blowing from the Pacific, coupled with a large diurnal temperature swing, cause vines to struggle, which may make for difficult farming but ultimately concentrates the fruit. Bryce Wiatrak, San Francisco Chronicle, "Community of small growers emerges on Cupertino’s Montebello Road," 28 Feb. 2018 The official Coachella Day Club has brought the diurnal ruckus to nearby Palm Springs with top-notch electronic music talent since 2014. Kat Bein, Billboard, "ODESZA, AC Slater, Illenium & More Announced for Coachella Day Club 2018," 26 Feb. 2018 Most moths are nocturnal; butterflies are essentially moths that have evolved to be diurnal, or active during the day, says Robert Robbins, a curator of lepidoptera at the National Museum of Natural History. Anna Diamond, Smithsonian, "What’s the Difference Between Moths and Butterflies and More Questions From Our Readers," 19 Apr. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'diurnal.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of diurnal


14th century, in the meaning defined at sense 1a


1600, in the meaning defined at sense 1

History and Etymology for diurnal


Middle English, from Latin diurnalis — more at journal


see diurnal entry 1

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The first known use of diurnal was in the 14th century

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More Definitions for diurnal



English Language Learners Definition of diurnal

: active mainly during the day

: happening every day


di·​ur·​nal | \dī-ˈərn-ᵊl \

Medical Definition of diurnal 

1 : having a daily cycle diurnal rhythms

2a : of, relating to, or occurring in the daytime diurnal activity

b : chiefly active during the daytime diurnal mosquitoes

Other Words from diurnal

diurnally \ -​ᵊl-​ē \ adverb

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Comments on diurnal

What made you want to look up diurnal? Please tell us where you read or heard it (including the quote, if possible).


obstinately defiant of authority

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