workday n.

Old English weorc, worc "something done, discrete act performed by someone, action (whether voluntary or required), proceeding, business; that which is made or manufactured, products of labor," also "physical labor, toil; skilled trade, craft, or occupation; opportunity of expending labor in some useful or remunerative way;" also "military fortification." This is from Proto-Germanic *werka- "work" (source also of Old Saxon, Old Frisian, Dutch werk, Old Norse verk, Middle Dutch warc, Old High German werah, German Werk, Gothic gawaurki), from PIE *werg-o-, a suffixed form of the root *werg- "to do."

The meaning "physical effort, exertion" is from c. 1200; that of "scholarly labor" or its productions is from c. 1200; the meaning "artistic labor" or its productions is from c. 1200. The sense of "labor as a measurable commodity" is from c. 1300. The meaning "embroidery, stitchery, needlepoint" is from late 14c.

Work of art attested by 1774 as "artistic creation," earlier (1728) "artifice, production of humans (as opposed to nature)." Work ethic recorded from 1959. To be out of work "unemployed" is from 1590s. To make clean work of is from c. 1300; to make short work of is from 1640s.

Proverbial expression many hands make light work is from c. 1300. To have (one's) work cut out for one is from 1610s; to have it prepared and prescribed, hence, to have all one can handle. Work in progress is from 1930 in a general sense, earlier as a specific term in accountancy and parliamentary procedure.

Work is less boring than amusing oneself. [Baudelaire, "Mon Coeur mis a nu," 1862]

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.

c. 1200, werkedei (n.), "day designated for labor rather than religious observance or rest," from Old Norse virkr dagr "working day;" see work (n.) + day. It passed into an adjective 16c.