Etymology
Advertisement
*agh- 
Proto-Indo-European root meaning "a day" (as a unit of time). The initial d- in Germanic is of obscure origin.

It forms all or part of: adays; Bundestag; daily; daisy; dawn; day; holiday; Reichstag; today.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit dah "to burn," Lithuanian dagas "hot season," Old Prussian dagis "summer."
Related entries & more 
Advertisement
Reichstag (n.)

1867 as the name of parliaments in central European nations, especially "the German imperial parliament" (1871-1918), from German Reichstag, from Reich "state, realm" (see Reich) + Tag "assembly," literally "day" (see day).

Earliest use in English is in reference to the chief deliberative body of the North German Confederacy. Also later as the name of the building (opened in 1894) in Berlin in which the imperial parliament met; hence Reichstag Fire (which took place Feb. 27, 1933) as symbolic of a disruptive act engineered to facilitate the rise of a party to power.

Related entries & more 
Sunday (n.)

first day of the week, Old English sunnandæg (Northumbrian sunnadæg), literally "day of the sun," from sunnan, oblique case of sunne "sun" (see sun (n.)) + dæg "day" (see day). A Germanic loan-translation of Latin dies solis "day of the sun," which is itself a loan-translation of Greek hēmera heliou. Compare Old Saxon sunnun dag, Old Frisian sunnandei, Old Norse sunnundagr, Dutch zondag, German Sonntag "Sunday."

In European Christian cultures outside Germanic often with a name meaning "the Lord's Day" (Latin Dominica). Sunday-school dates from 1783 (originally for secular instruction); Sunday clothes is from 1640s. Sunday driver is from 1925.

Related entries & more 
doomsday (n.)

"day of the last judgment," Middle English domesdai, from Old English domes dæg, from domes, genitive of dom (see doom (n.)) + dæg "day" (see day (n.)).

In medieval England doomsday was expected when the world's age had reached 6,000 years from the creation, which was thought to have been in 5200 B.C.E. Bede, c. 720, complained of being pestered by rustici asking him how many years till the sixth millennium ended. However there is no evidence for the story of a general panic in Christian Europe in the year 1000 C.E.

Doomsday machine as the name of a hypothetical nuclear bomb powerful enough to wipe out human life (or all life) on earth is from 1960.

Related entries & more 
today (adv.)
Old English todæge, to dæge "on (this) day," from to "at, on" (see to) + dæge, dative of dæg "day" (see day). Meaning "in modern times" is from c. 1300. As a noun from 1530s. Generally written as two words until 16c., after which it usually was written to-day until early 20c.

Similar constructions exist in other Germanic languages, such as Dutch van daag "from-day," Danish and Swedish i dag "in day." German heute is from Old High German hiutu, from Proto-Germanic *hiu tagu "on (this) day," with first element from PIE pronominal stem *ki-, represented by Latin cis "on this side."
Related entries & more 
Advertisement
Tuesday (n.)

third day of the week, Old English tiwesdæg, from Tiwes, genitive of Tiw "Tiu," from Proto-Germanic *Tiwaz "god of the sky," the original supreme deity of ancient Germanic mythology, differentiated specifically as Tiu, ancient Germanic god of war, from PIE *deiwos "god," from root *dyeu- "to shine," in derivatives "sky, heaven, god." Cognate with Old Frisian tiesdei, Old Norse tysdagr, Swedish tisdag, Old High German ziestag.

The day name (second element dæg, see day) is a translation of Latin dies Martis (source of Italian martedi, French Mardi) "Day of Mars," from the Roman god of war, who was identified with Germanic Tiw (though etymologically Tiw is related to Zeus), itself a loan-translation of Greek Areos hēmera. In cognate German Dienstag and Dutch Dinsdag, the first element would appear to be Germanic ding, þing "public assembly," but it is now thought to be from Thinxus, one of the names of the war-god in Latin inscriptions.

Related entries & more 
Monday (n.)

second day of the week, Middle English monedai, from Old English mōndæg, contraction of mōnandæg "Monday," literally "day of the moon," from mona (genitive monan; see moon (n.)) + dæg (see day). A common Germanic name (compare Old Norse manandagr, Old Frisian monendei, Dutch maandag, German Montag). All are loan-translations of Late Latin Lunæ dies, which also is the source of the day name in Romance languages (French lundi, Italian lunedi, Spanish lunes), itself a loan-translation of Greek Selēnēs hēmera. The name for this day in Slavic tongues generally means "day after Sunday."

Yf cristemas day on A munday be,
Grete wynter þat yere ye shull see.
[proverb, c. 1500]

Phrase Monday morning quarterback is attested from 1932, Monday being the first day back at work after the weekend, where school and college football games played over the weekend were discussed. Black Monday (late 14c.) is the Monday after Easter day, though how it got its reputation for bad luck is a mystery (none of the usual explanation stories holds water). Saint Monday (1753) was "used with reference to the practice among workmen of being idle Monday, as a consequence of drunkenness on the Sunday" before [OED]. Clergymen, meanwhile, when indisposed complained of feeling Mondayish (1804) in reference to effects of Sunday's labors.

Related entries & more 
Saturday (n.)

seventh or last day of the week, Old English sæterdæg, sæternesdæg, literally "day of the planet Saturn," from Sæternes (genitive of Sætern; see Saturn) + Old English dæg (see day). Partial loan-translation of Latin Saturni dies "Saturn's day" (compare Dutch Zaterdag, Old Frisian Saterdi, Middle Low German Satersdach; Irish dia Sathuirn, Welsh dydd Sadwrn). The Latin word itself is a loan-translation of Greek kronou hēmera, literally "the day of Cronus."

German Samstag (Old High German sambaztag) appears to be from a Greek *sambaton, a nasalized colloquial form of sabbaton "sabbath" (see Sabbath), which also yielded Old Church Slavonic sabota, Polish sobota, Russian subbota, Hungarian szombat, French samedi.

Unlike other English day names there was no Germanic substitution, perhaps because the northern European pantheon lacks a match to Roman Saturn. A homely ancient Nordic custom seems to be preserved in Old Norse day names laugardagr, Danish lørdag, Swedish lördag "Saturday," literally "bath day" (Old Norse laug "bath").

Saturday night has been figurative of revelry and especially "drunkenness and  looseness in relations between the young men and young women" ["Clara Hopwood"] at least since 1847. Saturday-night special "cheap, low-caliber handgun" is American English, attested from 1976 (earlier Saturday-night pistol, 1929).

Related entries & more 
daisy (n.)

common wildflower of Europe, growing in pastures and on mountainsides and cultivated in gardens, c. 1300, daiseie, from Old English dægesege, from dæges eage "day's eye;" see day (n.) + eye (n.). So called because the petals open at dawn and close at dusk. In Medieval Latin it was solis oculus "sun's eye." The use of dais eye for "the sun" is attested from early 15c.

Applied to similar plants in America, Australia, New Zealand. As a female proper name said to have been originally a pet form of Margaret (q.v.). Slang sense of "anything pretty, charming, or excellent" is by 1757.

Daisy-cutter first attested 1791, originally "a trotting horse," especially one that trots with low steps; later of cricket (1889) and baseball hits that skim along the ground. Daisy-chain is used in various figurative senses from 1856; the "group sex" sense is attested by 1941. Daisy-wheel for a removable printing unit in the form of a flat wheel is attested by 1974. Pushing up daisies "dead" is World War I soldier's slang from 1917 (see push (v.)), but variants with the same meaning go back to 1842.

Related entries & more 
nycthemeron (n.)

"the whole natural day, a day and a night, twenty-four hours," 1680s, from Greek nykhthēmeron "a day and a night," from nykt-, a combining form of nyx "night" (see night) + hēmera "day," from PIE *Hehmer "day."

Related entries & more 

Page 5