You can use D-day to refer to the day that is chosen for the beginning of an important activity.
a conventional expression of greeting or farewell used during the day
the day on which mobilization for war begins
a day nominated to celebrate victory, as in V-E Day or V-J Day in World War II
a day when someone performs well
available throughout the day
a narrow bed, with a head piece and sometimes a foot piece and back, on which to recline during the day
a boy who attends a boarding school daily, but returns home each evening
Day-Glo colours are shades of orange, pink, green, and yellow which are so bright that they seem to glow .
the job that a person during the day to earn a living, as opposed to some more glamorous activity such as being a singer, dancer, actor, writer that they aspire to make their main source of income
A day off is a day when you do not go to work, even though it is usually a working day.
having been in existence or alive for one day
If something happens from day one of a process, it happens right from the beginning. If it happens on day one, it happens right at the beginning.
A health spa is a kind of hotel where people go to do exercise and have special treatments in order to improve their health.
any of the days allowed for loading or unloading a ship without payment of extra charge
a day regarded as the number of hours work one person can complete in a day
May Day is the 1st of May, which in many countries is celebrated as a public holiday, especially as one in honour of working people.
If someone has an off day, they do not perform as well as usual.
One day or some day or one of these days means at some time in the future .
Pay day is the day of the week or month on which you receive your wages or salary .
relating to an allowance for daily expenses, usually those incurred while working
a single fine day during a period of bad weather
a day on which money is publicly solicited as for some charity, each contributor being given a tag
25 April, a public holiday in Australia and New Zealand commemorating the Anzac landing at Gallipoli in 1915
a tree-planting day observed individually by the states of the U.S., usually in spring
the period of time, the calendar day, of 24 hours ' duration reckoned from one midnight to the next
Day care is care that is provided during the day for people who cannot look after themselves, such as small children, old people, or people who are ill . Day care is provided by paid workers .
a patient or case that comes into hospital for a surgical procedure and is dealt with and released in the course of one day
the time after first dawn when the sun begins to shine ; clear daybreak
a girl who attends a boarding school daily, but returns home each evening
C ( ecil ). 1904–72, British poet, critic, and (under the pen name Nicholas Blake ) author of detective stories ; poet laureate (1968–72)
any widely cultivated Eurasian liliaceous plant of the genus Hemerocallis, having large yellow, orange, or red lily-like flowers, which typically last for only one day and are immediately succeeded by others
a name indicating a person's day of birth
a nurse who is on duty during the daytime
a ticket that, once bought, enables you to use, travel on or access something free for one day
a pupil at a boarding school who attends lessons during the day but does not sleep at the school
A day room is a room in a hospital where patients can sit and relax during the day.
a group of workers who work a shift during the daytime in an industry or occupation where a night shift or a back shift is also worked
A day trip is a journey to a place and back again on the same day, usually for pleasure .
a day of leave from work that an employee is allowed to take at short notice
April 22, a day on which environmentalist concerns are variously acknowledged
any of the days in the quarterly three-day period of prayer and fasting (the Wednesday, Friday, and Saturday after the first Sunday in Lent, after Whitsunday, after Sept . 14, and after Dec. 13) observed in the Roman Catholic Church and other Western churches
a religious holy day, etc. observed by fasting
→ feast (sense 1 )
a day spent in some special outdoor activity, such as nature study or sport
In Britain, a flag day is a day on which people collect money for a charity from people in the street . People are given a small sticker to wear to show that they have given money.
a day of sports, entertainment, etc, often organized in order to raise money for a charity, cause, school, etc
People sometimes say ' Good day ' instead of 'Hello' or 'Goodbye'.
A half-day is a day when you work only in the morning or in the afternoon, but not all day.