di·ur·nal
dī-ˈər-nᵊl 
1
a
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
2
a
: recurring every day
diurnal tasks
b
: having a daily cycle
diurnal tides
1
Examples of diurnal in a Sentence
Adjective
a love as constant and certain as the diurnal tides
Noun
a collection of diurnals containing essays by preeminent 19th-century American writers and thinkers
Recent Examples on the Web
Scott Travers, Forbes.com, 15 June 2025
Here, temperature swings between day and night—diurnal variation—can be wide, favoring the evolution of acidity in grapes during cool nights.
—Tom Mullen, Forbes.com, 1 June 2025
Natasha Gural, Forbes.com, 5 May 2025
See All Example Sentences for diurnal
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Adjective
Flying at night provides more stable, less turbulent air and may reduce the risk of predation from diurnal raptors.
—Scott Travers, Forbes.com, 15 June 2025
Here, temperature swings between day and night—diurnal variation—can be wide, favoring the evolution of acidity in grapes during cool nights.
—Tom Mullen, Forbes.com, 1 June 2025
Noun
The exhibition welcomes us into diurnal at the street-level, and leads us into the nocturnal in the downstairs galleries.
—Natasha Gural, Forbes.com, 5 May 2025
See All Example Sentences for diurnal
Cite this Entry
“Diurnal.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/diurnal. Accessed 8 Jul. 2025.
Copy CitationMedical Definition
diurnal
adjective
di·ur·nal
dī-ˈərn-ᵊl
1
: having a daily cycle
diurnal rhythms
2
a
: of, relating to, or occurring in the daytime
diurnal activity
b
: chiefly active during the daytime
diurnal mosquitoes
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