di·​ur·​nal | \ dī-ˈər-nᵊl How to pronounce diurnal (audio) \

Definition of diurnal

 (Entry 1 of 2)

1a biology : active chiefly in the daytime diurnal animals
b : of, relating to, or occurring in the daytime the city's diurnal noises
c botany : opening during the day and closing at night diurnal flowers
2a : recurring every day diurnal tasks
b : having a daily cycle diurnal tides



Definition of diurnal (Entry 2 of 2)

2 archaic : diary, daybook

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Other Words from diurnal


diurnally \ dī-​ˈər-​nᵊl-​ē How to pronounce diurnal (audio) \ adverb

Examples of diurnal in a Sentence

Adjective a love as constant and certain as the diurnal tides Noun a microfilm containing a collection of diurnals published by 19th-century American abolitionists
Recent Examples on the Web: Adjective Spirits matured at higher elevations are subject to more variation in diurnal temperatures and barometric pressure. Joseph V Micallef, Forbes, 23 Sep. 2021 The sharp diurnal temperature variation typical of desert areas, plus the region’s persistent winds, help preserve acidity. Joseph V Micallef, Forbes, 2 Sep. 2021 The glow may serve as a homing signal to help the diurnal wasps find their way back to the nest at dawn and dusk—a time when there’s a bit of UV light from the Sun, but the environment is still mostly dark. David Shultz, Science | AAAS, 24 Aug. 2021 Humans are diurnal creatures, meant to be awake during the day and to wind down at night. Sara Harrison, Wired, 5 July 2021 Folklore from Scandinavia and Asia to the Americas depicts these events as a battle between light and dark, with the moon (or other malevolent actors like wolves, bears, frogs, or dragons) seeking to depose the diurnal status quo. John Bowe, Travel + Leisure, 5 June 2021 Measurements are taken in the morning, afternoon and evening to accurately capture the diurnal warming of a city. Haley Brink And Derek Van Dam, CNN, 2 June 2021 The diurnal vertical migration includes trillions of tiny animals, many in the larval stage, that rise from depths of 1,000 feet or more to just beneath the surface to feed. Erik Olsen New York Times, Star Tribune, 15 Apr. 2021 The diurnal vertical migration includes trillions of tiny animals, many in the larval stage, that rise from great depths of 1,000 feet or more to just beneath the surface to feed. New York Times, 30 Mar. 2021

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 2a


1600, in the meaning defined at sense 2

History and Etymology for diurnal


Middle English, from Latin diurnalis — more at journal


derivative of diurnal entry 1

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

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Dictionary Entries Near diurnal



diurnal arc

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Last Updated

5 Oct 2021

Cite this Entry

“Diurnal.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/diurnal. Accessed 24 Oct. 2021.

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English Language Learners Definition of diurnal

: active mainly during the day
: happening every day


di·​ur·​nal | \ dī-ˈərn-ᵊl How to pronounce diurnal (audio) \

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 How to pronounce diurnal (audio) \ adverb

More from Merriam-Webster on diurnal

Nglish: Translation of diurnal for Spanish Speakers

Britannica English: Translation of diurnal for Arabic Speakers


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