A day is a 24-hour period, or the length of time it takes the Earth to rotate fully on its axis. There are 365 days in a year, and 31 days in the month of January.

Most work weeks last five days, and an ordinary weekend gives you two days of freedom before you go back to work or school. Day can also mean the opposite of night, or the time when the sun is up and you're awake. If your grandpa starts his stories with, "Back in my day..." he means an era or a period of time in the past. The Old English root, dæg, means both "day" and "lifetime."

Definitions of day

n 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
24-hour interval, mean solar day, solar day, twenty-four hour period, twenty-four hours
6 June 1944
date of the Allied landing in France, World War II
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the day after today
the day that includes the present moment (as opposed to yesterday or tomorrow)
the day immediately before today
the next day
the day before
date, day of the month
the specified day of the month
a particular day specified as the time something happens
due date, maturity, maturity date
the date on which an obligation must be repaid
future date
a particular day in the future that is specified as the time something will happen
rain date
an alternative date set for some outdoor event in case it rains on the appointed date
sell-by date
a date stamped on perishable produce indicating the date by which it should be sold
birthday, natal day
the date on which a person was born
Type of:
time unit, unit of time
a unit for measuring time periods

n 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?”
lunar day
the period of time taken for the moon to make one full rotation on its axis (about 27.3 sidereal days)
Type of:
period, period of time, time period
an amount of time

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

sidereal day
Type of:
time unit, unit of time
a unit for measuring time periods
sidereal time
measured by the diurnal motion of stars

n the time after sunrise and before sunset while it is light outside

“the dawn turned night into day
daylight, daytime
dark, night, nighttime
the time after sunset and before sunrise while it is dark outside
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the part of the day between noon and evening
the middle part of the afternoon
eve, even, evening, eventide
the latter part of the day (the period of decreasing daylight from late afternoon until nightfall)
guest night
an evening when members of a club or college can bring their friends as guests
Type of:
period, period of time, time period
an amount of time

n 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”
workday, working day
the amount of time that a worker must work for an agreed daily wage
Type of:
work time
a time period when you are required to work

n 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”
Day of Judgement, Day of Judgment, Doomsday, Judgement Day, Judgment Day, Last Day, Last Judgement, Last Judgment, crack of doom, day of reckoning, doomsday, end of the world, eschaton
(New Testament) day at the end of time following Armageddon when God will decree the fates of all individual humans according to the good and evil of their earthly lives
a day when things go poorly
Type of:
an indefinite period (usually marked by specific attributes or activities)

n a day assigned to a particular purpose or observance

8 May 1945
the date of Allied victory in Europe, World War II
15 August 1945
the date of Allied victory over Japan, World War II
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Admission Day
in some states of the United States: a legal holiday commemorating the day the state was admitted to the Union
Arbor Day
a day designated for planting trees
Cinco de Mayo
the fifth of May which is observed in Mexico and Mexican-American communities in the United States to commemorate the Mexican victory over the French in the Battle of Puebla in 1862
commencement day, degree day
the day on which university degrees are conferred
November 5
anniversary of the discovery of the Gunpowder Plot
Inauguration Day, January 20
the day designated for inauguration of the United States President
February 29, bissextile day, leap day
the name of the day that is added during a leap year
V-day, Victory Day
the day of a victory
rag day
a day on which university students hold a rag
red-letter day
a memorably happy or noteworthy day (from the custom of marking holy days in red on church calendars)
the day on which you receive pay for your work
election day, polling day
the day appointed for an election; in the United States it is the 1st Tuesday after the 1st Monday in November
field day
a day for outdoor athletic competition
field day
(military) a day for military exercises and display
in the Roman calendar: the 15th of March or May or July or October or the 13th of any other month
market day
a fixed day for holding a public market
Walpurgis Night
eve of May Day
December 31, New Year's Eve
the last day of the year
January 19, Lee's Birthday, Robert E Lee Day, Robert E Lee's Birthday
celebrated in southern United States
the New Year in Vietnam; observed for three days after the first full moon after January 20th
a day on which work is suspended by law or custom
February 2, Groundhog Day
if the ground hog emerges and sees his shadow on this day, there will be 6 more weeks of winter
February 12, Lincoln's Birthday
the day on which President Abraham Lincoln is remembered
February 14, Saint Valentine's Day, St Valentine's Day, Valentine Day, Valentine's Day
a day for the exchange of tokens of affection
February 22, Washington's Birthday
the day on which George Washington is remembered
March 2, Texas Independence Day
Texans celebrate the anniversary of Texas' declaration of independence from Mexico in 1836
March 17, Saint Patrick's Day, St Patrick's Day
a day observed by the Irish to commemorate the patron saint of Ireland
All Fools' day, April Fools', April Fools' day
the first day of April which is celebrated by playing practical jokes
April 14, Pan American Day
a day celebrating political and economic unity among American countries
Patriot's Day
the 3rd Monday in April; Massachusetts and Maine celebrate the battle of Lexington and Concord in 1775
First of May, May 1, May Day
observed in many countries to celebrate the coming of spring; observed in Russia and related countries in honor of labor
Mother's Day
second Sunday in May
Armed Forces Day
the 3rd Saturday in May
Davis' Birthday, Jefferson Davis' Birthday, June 3
celebrated in southern United States
Flag Day, June 14
commemorating the adoption of the United States flag in 1777
Father's Day
US: third Sunday in June
Citizenship Day, September 17
celebrated in the United States
American Indian Day
US: the 4th Friday in September
October 24, United Nations Day
a day for celebrating the founding of the United Nations
Allhallows Eve, Hallowe'en, Halloween
the evening before All Saints' Day; often devoted to pranks played by young people
saint's day
a day commemorating a saint
June 23, Midsummer Eve, Midsummer Night, St John's Eve, St John's Night
the night before Midsummer Day
school day
any day on which school is in session
speech day
an annual day in the schools when speeches are made and prizes are distributed
washday, washing day
a day set aside for doing household laundry
wedding day
the day of a wedding
anniversary, day of remembrance
the date on which an event occurred in some previous year (or the celebration of it)
a day on which half is free from work or duty
Guy Fawkes Day
day for the celebration of the discovery of the Gunpowder Plot
Bonfire Night, Guy Fawkes Night
effigies of Guy Fawkes are burned on this night
feast day, fete day
a day designated for feasting
New Year's Eve in Scotland
holy day, religious holiday
a day specified for religious observance
Christmas Eve, Dec 24
the day before Christmas
legal holiday, national holiday, public holiday
authorized by law and limiting work or official business
Poppy Day, Remembrance Day, Remembrance Sunday
the Sunday nearest to November 11 when those who died in World War I and World War II are commemorated
Hindu lunar holiday (on the 9th day of Caitra) to celebrate the birth of Rama
Hindu solar holiday at the beginning of the new astrological year when the sun enters the constellation Aries
name day
the feast day of a saint whose name one bears
an anniversary of the day on which a person was born (or the celebration of it)
a special anniversary (or the celebration of it)
wedding anniversary
the anniversary of the day on which you were married (or the celebration of it)
semicentenary, semicentennial
the 50th anniversary (or the celebration of it)
centenary, centennial
the 100th anniversary (or the celebration of it)
the 150th anniversary (or the celebration of it)
bicentenary, bicentennial
the 200th anniversary (or the celebration of it)
tercentenary, tercentennial, triennial
the 300th anniversary (or the celebration of it)
quatercentenary, quatercentennial
the 400th anniversary (or the celebration of it)
quincentenary, quincentennial
the 500th anniversary (or the celebration of it)
millenary, millennium
the 1000th anniversary (or the celebration of it)
bimillenary, bimillennium
the 2000th anniversary (or the celebration of it)
Type of:
calendar day, civil day
a day reckoned from midnight to midnight

n 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
Type of:
epoch, era
a period marked by distinctive character or reckoned from a fixed point or event

n a period of opportunity

“he deserves his day in court”
“every dog has his day
Type of:
chance, opportunity
a possibility due to a favorable combination of circumstances

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