Old English weorcdæg, from work (n.) + day (n.), but this apparently meant "day when work was suspended," as it glosses Latin feria. The modern word is perhaps a Middle English re-formation. As an adjective (c. 1500) it has generally only the literal sense (compare workaday).

also mid-day, "the middle of the day," from Old English middæg "midday, noon," contracted from midne dæg; see mid (adj.) + day. Similar formation in Old Frisian middei, Dutch middag, Old High German mittitag, German Mittag, Old Norse miðdagr. As an adjective, "of or pertaining to midday," from early 14c.

"at some indefinite future date," 1768, from some + day. As two words, in the same sense, from late 14c.

MISS SOMEDAY.

Poor Charley wooed, but wooed in vain,

From Monday until Sunday;

Still Cupid whisper'd to the swain

"You'll conquer Betsey Someday."

[The Port Folio, June 1816]

c. 1300 (as two words from mid-12c., daies liht), "the light of day," from day + light (n.); its figurative sense of "clearly visible open space between two things" (1820) has been used in references to boats in a race, U.S. football running backs avoiding opposing tackles, a rider and a saddle, and the rim of a glass and the surface of the liquor. The (living) daylights that you beat or scare out of someone were originally slang for "the eyes" (1752), extended figuratively to the vital senses. Daylight-saving is attested by 1908.

"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.