diurnal

American  

[dahy-ur-nl] / daɪˈɜr nl /

adjective

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).

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noun

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.

diurnal British  

/ daɪˈɜːnəl /

adjective

1. happening during the day or daily

2. (of flowers) open during the day and closed at night

3. (of animals) active during the day Compare nocturnal

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noun

1. a service book containing all the canonical hours except matins

diurnal Scientific  

/ dī-ûr′nəl /

1. 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.

2. Most active during the daytime. Many animals, including the apes, are diurnal.

3. Having leaves or flowers that open in daylight and close at night. The morning glory and crocus are diurnal.

4. Compare nocturnal

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Other Word Forms

• diurnally adverb
• diurnalness noun
• transdiurnal adjective
• undiurnal adjective
• undiurnally adverb

Etymology

Origin of diurnal

1400–50; late Middle English < Latin diurnālis, equivalent to diurn ( us ) daily + -ālis -al ¹

Explanation

If it’s 9:00 at night and your mom wants you to do the dishes, you could try to put it off until the next day by politely pointing out that you are a diurnal animal. That means you get most of your activities done during the day. The adjective diurnal can be used to describe anything that takes place in the daytime, but it is most often used in the field of biology to describe animals that are active during the day and then sleep at night. Animals with the opposite schedule are said to be nocturnal, which means they’re active at night and sleep in the daytime. Diurnal can also be used to describe something that has a daily cycle, such as a diurnal tide that occurs once each day.

Example Sentences

In studies involving mice, Borniger's lab discovered that breast cancer interferes with normal diurnal rhythms, meaning the natural day and night cycle of stress hormone release.

From Science Daily • Jan. 18, 2026

Despite the warmth in the daytime, this has been at odds with the night-time temperatures with a huge difference between - what weather forecasters call diurnal range.

From BBC • Mar. 7, 2025

Wilder’s drama, offering a guided tour of an ordinary town going about its diurnal business, reminds us, through the inescapable shadow of mortality, of what we have in common.

From Los Angeles Times • Nov. 12, 2024

Yellow-bellied marmots are an excellent study system because they are diurnal, or active during the day, and they have an address.

From Salon • Oct. 23, 2024

They trade normal diurnal rhythms for the perk of having very little inmate contact—at night, all the inmates are locked in their cells.

From "Newjack: Guarding Sing Sing" by Ted Conover

Related Words

• constantly
• day-to-day
• everyday
• often
• periodic
• regular
• regularly
• routine