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1) day, twenty-four hours, twenty-four hour period, 24-hour interval, solar day, mean solar day: time for Earth to make a complete rotation on its axis; “two days later they left”; “they put on two performances every day”; “there are 30,000 passengers per day”

2) day: some point or period in time; “it should arrive any day now”; “after that day she never trusted him again”; “those were the days”; “these days it is not unusual”

3) day, daytime, daylight: the time after sunrise and before sunset while it is light outside; “the dawn turned night into day”; “it is easier to make the repairs in the daytime”

Image of daytime
Image of daytime

4) day: a day assigned to a particular purpose or observance; “Mother’s Day”

5) day: the recurring hours when you are not sleeping (especially those when you are working); “my day began early this morning”; “it was a busy day on the stock exchange”; “she called it a day and went to bed

6) day: an era of existence or influence; “in the day of the dinosaurs”; “in the days of the Roman Empire”; “in the days of sailing ships”; “he was a successful pianist in his day”

7) day: a period of opportunity; “he deserves his day in court”; “every dog has his day”

8) day: the period of time taken by a particular planet (e.g. Mars) to make a complete rotation on its axis; “how long is a day on Jupiter?”

9) sidereal day, day: the time for one complete rotation of the earth relative to a particular star, about 4 minutes shorter than a mean solar day

10) Day, Clarence Day, Clarence Shepard Day Jr: United States writer best known for his autobiographical works (1874-1935)

noun day has 10 sense(s) (first 8 from tagged texts)

day (Wikipedia)
For other uses, see Day (disambiguation).
Water, Rabbit, and Deer: three of the 20 day symbols in the Aztec calendar, from the Aztec calendar stone

A day is a unit of time. In common usage, it is an interval equal to 24 hours. It also can mean the consecutive period of time during which the Sun is above the horizon of a location, also known as daytime. The period of time during which the Earth completes one rotation with respect to the sun is called a solar day.

Several definitions of this universal human concept are used according to context, need and convenience. In 1967, the second was redefined in terms of the wavelength of light, and it became the SI base unit of time. The unit of measurement for time called "day", redefined in 1967 as 86,400 SI seconds and symbolized d, is not an SI unit, but it is accepted for use with SI. A civil day is usually also 86,400 seconds, plus or minus a possible leap second in Coordinated Universal Time UTC, and, in some locations, occasionally plus or minus an hour when changing from or to daylight saving time. The word day may also refer to a day of the week or to a calendar date, as in answer to the question "On which day?" Day also refers to the part of the day that is not night — also known as daytime. The life patterns of humans and many other species are related to Earth's solar day and the cycle of day and night (see circadian rhythms).

In recent decades the average length of a solar day on Earth has been about 86 400.002 seconds (24.0000006 hours) and there are about 365.2422 solar days in one mean tropical year. Because celestial orbits are not perfectly circular, and thus objects travel at different speeds at various positions in their orbit, a solar day is not the same length of time throughout the orbital year. A day, understood as the span of time it takes for the Earth to make one entire rotation

with respect to the celestial background or a distant star (assumed to be fixed), is called a stellar day. This period of rotation is about 4 minutes less than 24 hours (23 hours 56 minutes and 4.1 seconds) and there are about 366.2422 in one mean tropical year (one more stellar day than the number of solar days). Mainly due to tidal effects, the Earth's rotational period is not constant, resulting in further minor variations for both solar days and stellar "days". Other planets and moons also have stellar and solar days.

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