☞ Shakespeare has “alack the day” and “alack the heavy day.” Compare “woe worth the day.” [ 1913 Webster ]

The first of April, some do say,
Is set apart for All Fools' Day. Poor Robin's Almanack (1760). [ 1913 Webster ]

Those barbarous ages past, succeeded next
The birthday of invention. Cowper. [ 1913 Webster ]

2. The day of the month in which a person was born, in whatever succeeding year it may recur; the anniversary of one's birth. [ 1913 Webster ]

This is my birthday; as this very day
Was Cassius born. Shak. [ 1913 Webster ]

The last week of October 1929 remains forever imprinted in the American memory.
It was, of course, the week of the Great Crash, the stock market collapse that signaled the collapse of the world economy and the Great Depression of the 1930s. From an all-time high of 381 in early September 1929, the Dow Jones Industrial Average drifted down to a level of 326 on October 22, then, in a series of traumatic selling waves, to 230 in the course of the following six trading days.
The stock market's drop was far from over; it continued its sickening slide for nearly three more years, reaching an ultimate low of 41 in July 1932. But it was that last week of October 1929 that burned itself into the American consciousness. After a decade of unprecedented boom and prosperity, there suddenly was panic, fear, a yawning gap in the American fabric. The party was over. Wall street Journal, October 28, 1977 [ PJC ]

Then it was not for nothing that my nose fell a bleeding on Black Monday last. Shak. [ 1913 Webster ]

2. The first Monday after the holidays; -- so called by English schoolboys. Halliwell. [ 1913 Webster ]

2. The period of the earth's revolution on its axis. -- ordinarily divided into twenty-four hours. It is measured by the interval between two successive transits of a celestial body over the same meridian, and takes a specific name from that of the body. Thus, if this is the sun, the day (the interval between two successive transits of the sun's center over the same meridian) is called a solar day; if it is a star, a sidereal day; if it is the moon, a lunar day. See Civil day, Sidereal day, below. [ 1913 Webster ]

3. Those hours, or the daily recurring period, allotted by usage or law for work. [ 1913 Webster ]

4. A specified time or period; time, considered with reference to the existence or prominence of a person or thing; age; time. [ 1913 Webster ]

A man who was great among the Hellenes of his day. Jowett (Thucyd. ) [ 1913 Webster ]

If my debtors do not keep their day, . . .
I must with patience all the terms attend. Dryden. [ 1913 Webster ]

5. (Preceded by the) Some day in particular, as some day of contest, some anniversary, etc. [ 1913 Webster ]

The field of Agincourt,
Fought on the day of Crispin Crispianus. Shak. [ 1913 Webster ]

His name struck fear, his conduct won the day. Roscommon. [ 1913 Webster ]

☞ Day is much used in self-explaining compounds; as, daybreak, daylight, workday, etc. [ 1913 Webster ]

Anniversary day. See Anniversary, n. --
Astronomical day, a period equal to the mean solar day, but beginning at noon instead of at midnight, its twenty-four hours being numbered from 1 to 24; also, the sidereal day, as that most used by astronomers. --
Born days. See under Born. --
Canicular days. See Dog day. --
Civil day, the mean solar day, used in the ordinary reckoning of time, and among most modern nations beginning at mean midnight; its hours are usually numbered in two series, each from 1 to 12. This is the period recognized by courts as constituting a day. The Babylonians and Hindoos began their day at sunrise, the Athenians and Jews at sunset, the ancient Egyptians and Romans at midnight. --
Day blindness. (Med.) See Nyctalopia. --
Day by day, or
Day after day, daily; every day; continually; without intermission of a day. See under By. “Day by day we magnify thee.” Book of Common Prayer. --
Days in bank (Eng. Law), certain stated days for the return of writs and the appearance of parties; -- so called because originally peculiar to the Court of Common Bench, or Bench (bank) as it was formerly termed. Burrill. --
Day in court, a day for the appearance of parties in a suit. --
Days of devotion (R. C. Ch.), certain festivals on which devotion leads the faithful to attend mass. Shipley. --
Days of grace. See Grace. --
Days of obligation (R. C. Ch.), festival days when it is obligatory on the faithful to attend Mass. Shipley. --
Day owl, (Zool.), an owl that flies by day. See Hawk owl. --
Day rule (Eng. Law), an order of court (now abolished) allowing a prisoner, under certain circumstances, to go beyond the prison limits for a single day. --
Day school, one which the pupils attend only in daytime, in distinction from a boarding school. --
Day sight. (Med.) See Hemeralopia. --
Day's work (Naut.), the account or reckoning of a ship's course for twenty-four hours, from noon to noon. --
From day to day, as time passes; in the course of time; as, he improves from day to day. --
Jewish day, the time between sunset and sunset. --
Mean solar day (Astron.), the mean or average of all the apparent solar days of the year. --
One day,
One of these days, at an uncertain time, usually of the future, rarely of the past; sooner or later. “Well, niece, I hope to see you one day fitted with a husband.” Shak. --
Only from day to day, without certainty of continuance; temporarily. Bacon. --
Sidereal day, the interval between two successive transits of the first point of Aries over the same meridian. The Sidereal day is 23 h. 56 m. 4.09 s. of mean solar time. --
To win the day, to gain the victory, to be successful. S. Butler. --
Week day, any day of the week except Sunday; a working day. --
Working day. (a) A day when work may be legally done, in distinction from Sundays and legal holidays. (b) The number of hours, determined by law or custom, during which a workman, hired at a stated price per day, must work to be entitled to a day's pay. [ 1913 Webster ]

2. a long chair; for reclining.
Syn. -- chaise longue, chaise. [ WordNet 1.5 ]

Mrs. Lambert's little daydream was over. Thackeray. [ 1913 Webster ]

2. pl. The eyes. [ Prov. Eng. ] Wright.

[ 1913 Webster ]

Neither is there any daysman betwixt us. Job ix. 33. [ 1913 Webster ]

The tender mercy of our God; whereby the dayspring from on high hath visited us. Luke i. 78. [ 1913 Webster ]

A dark place, until the day dawn, and the day-star arise in your hearts. 2 Peter i. 19. [ 1913 Webster ]

2. The sun, as the orb of day. [ Poetic ] [ 1913 Webster ]

So sinks the day-star in the ocean bed,
And yet anon repairs his drooping head,
And tricks his beams, and with new-spangled ore
Flames in the forehead of the morning sky. Milton. [ 1913 Webster ]

2. 6 June 1944, the day of the landing in France, by troops allied against the Germans in World War II.
Syn. -- 6 June 1944. [ WordNet 1.5 ]

3. the day for commencement or execution of any elaborate planned activity; -- often used jocosely. [ informal ] [ PJC ]