day

Etymology

From Middle English day, from Old English dæġ (“day”), from Proto-West Germanic *dag, from Proto-Germanic *dagaz (“day”); see there for more. Cognate with Saterland Frisian Dai (“day”), West Frisian dei (“day”), Dutch dag (“day”), German Low German Dag (“day”), Alemannic German Däi (“day”), German Tag (“day”), Swedish, Norwegian and Danish dag (“day”), Icelandic dagur (“day”), Gothic 𐌳𐌰𐌲𐍃 (dags, “day”). Possible cognates beyond Germanic relatives include Albanian djeg (“to burn”), Lithuanian degti (“to burn”), Tocharian A tsäk-, Russian жечь (žečʹ, “to burn”) from *degti, дёготь (djógotʹ, “tar, pitch”), Sanskrit दाह (dāhá, “heat”), दहति (dáhati, “to burn”), Latin foveō (“to warm, keep warm, incubate”). Latin diēs is a false cognate; it derives from Proto-Indo-European *dyew- (“to shine”).

noun

1. Any period of 24 hours.
   I've been here for two days and a bit.
2. (informal or meteorology) A 24-hour period beginning at 6am or sunrise.
   Your 8am forecast: The high for the day will be 30 and the low, before dawn, will be 10.
3. A period from midnight to the following midnight, into which a week, month, or year is divided, based on the rotation of the earth on its axis.
   The day begins at midnight.
   Monday is the first day of the week in many countries of the world.
4. (astronomy) Rotational period of a planet.
   A day on Mars is slightly over 24 hours.
5. The part of a day period which one spends at one’s job, school, etc.
   I worked two days last week.
   “[…]if you call my duds a ‘livery’ again there'll be trouble. It's bad enough to go around togged out like a life saver on a drill day, but I can stand that 'cause I'm paid for it. What I won't stand is to have them togs called a livery.[…]” 1913, Joseph C. Lincoln, chapter 7, in Mr. Pratt's Patients
6. Part of a day period between sunrise and sunset where one enjoys daylight; daytime.
   day and night;  I work at night and sleep during the day.
7. A specified time or period; time, considered with reference to the existence or prominence of a person or thing; age; time; era.
   every dog has its day; in that day; back in the day; in those days
   In his senior year, he had run across an old '66 Chevy Super Sport headed for the junkyard, bought it for a song, and overhauled it with his dad's help, turning it into the big red muscle car it was back in its day. 2011, Kat Martin, A Song for My Mother, Vanguard Press
8. A period of contention of a day or less.
   The day belonged to the Allies.
9. (Judaism) A time period from a nightfall until the following nightfall

verb

1. (rare, intransitive) To spend a day (in a place).
   I nighted and dayed in Damascus town[.] 1885, Richard F. Burton, chapter XXIII, in The Book of the Thousand Nights and a Night, volume I, The Burton Club, page 233