Words related to *agh-
"happening or being every day," mid-15c.; see day + -ly (1). Compare Old English dglic, a form found in compounds: twadglic "happening once in two days," reodglic "happening once in three days." The more usual Old English adjective was dghwamlic (also dgehwelc), which became Middle English daiwhamlich. Cognate with German tglich.
As an adverb, "every day, day by day," early 15c. (the Old English adverb was dghwamlice. As a noun, "a daily newspaper," by 1832.
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.
c. 1200, dauen, "to become day, grow light in the morning," shortened or back-formed from dauinge, dauing "period between darkness and sunrise," (c. 1200), from Old English dagung, from dagian "to become day," from Proto-Germanic *dagaz "day" (source also of German tagen "to dawn"), from PIE root *agh- "a day." Probably influenced by Scandinavian cognates (Danish dagning, Old Norse dagan "a dawning"). Related: Dawned; dawning.
Figurative sense "begin to develop" is from 1717. Of ideas, etc., "begin to become apparent or evident to the mind," by 1852.
Old English dæg "period during which the sun is above the horizon," also "lifetime, definite time of existence," from Proto-Germanic *dages- "day" (source also of Old Saxon, Middle Dutch, Dutch dag, Old Frisian di, dei, Old High German tag, German Tag, Old Norse dagr, Gothic dags), according to Watkins, from PIE root *agh- "a day." He adds that the Germanic initial d- is "of obscure origin." But Boutkan says it is from PIE root *dhegh- "to burn" (see fever). Not considered to be related to Latin dies (which is from PIE root *dyeu- "to shine").
Meaning originally, in English, "the daylight hours;" it expanded to mean "the 24-hour period" in late Anglo-Saxon times. The day formerly began at sunset, hence Old English Wodnesniht was what we would call "Tuesday night." Names of the weekdays were not regularly capitalized in English until 17c.
From late 12c. as "a time period as distinguished from other time periods." Day-by-day "daily" is from late 14c.; all day "all the time" is from late 14c. Day off "day away from work" is attested from 1883; day-tripper first recorded 1897. The days in nowadays, etc. is a relic of the Old English and Middle English use of the adverbial genitive.
All in a day's work "something unusual taken as routine" is by 1820. The nostalgic those were the days is attested by 1907. That'll be the day, expressing mild doubt following some boast or claim, is by 1941. To call it a day "stop working" is by 1919; earlier call it a half-day (1838). One of these days "at some day in the near future" is from late 15c. One of those days "a day of misfortune" is by 1936.
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.
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."