night-shift (n.)

late Old English niht (West Saxon neaht, Anglian næht, neht) "the dark part of a day; the night as a unit of time; darkness," also "absence of spiritual illumination, moral darkness, ignorance," from Proto-Germanic *nahts (source also of Old Saxon and Old High German naht, Old Frisian and Dutch nacht, German Nacht, Old Norse natt, Gothic nahts).

The Germanic words are from PIE *nekwt- "night" (source also of Greek nyx "a night," Latin nox, Old Irish nochd, Sanskrit naktam "at night," Lithuanian naktis "night," Old Church Slavonic nosti, Russian noch', Welsh henoid "tonight"), according to Watkins, probably from a verbal root *neg- "to be dark, be night." For spelling with -gh- see fight.  The vowel indicates that the modern English word derives from oblique cases (genitive nihte, dative niht).

The fact that the Aryans have a common name for night, but not for day (q.v.), is due to the fact that they reckoned by nights. [Weekley]

Thus in Old English combinations night was "the night before (a certain day or feast day);" compare German Weihnachten "Christmas," literally "holy night." In early times, the day was held to begin at sunset, so Old English monanniht "Monday night" was the night before Monday, or what we would call Sunday night; so saeterniht "Friday night." The Greeks, by contrast, counted their days by mornings.

To work nights preserves the Old English genitive of time. Night soil "excrement" (1770) is so called because it was removed (from cesspools, etc.) after dark. Night train is attested from 1838; night-school from 1520s; night-life "habitual nocturnal carousing" is attested from 1852.

"body garment, underclothing," 1590s, originally used alike of men's and women's garments, probably from shift (n.1), which was commonly used in reference to a change of clothes. In 17c., shift (n.) in this sense began to be used as a euphemism for smock, and was itself displaced, for similar reasons of delicacy, in 19c. by chemise.

c. 1300, "a movement, a beginning," from shift (v.); by mid-15c. as "an attempt, expedient, or means." This is the word in make shift "make efforts" (mid-15c.; see makeshift). The specific sense of "means to an end" is from 1520s, hence "a device, a trick." The sense of "change, alteration" in character, place, position, etc., is from 1560s.

The meaning "mechanism for changing gear in a motor vehicle" is recorded from 1914. Typewriter shift key is so called by 1893; its shift-lock is so called from 1899.

The meaning "period of working time" (originally in a mine) is attested from 1809, perhaps from or influenced by an older sense "relay of horses" (1708); perhaps also influenced by a North Sea Germanic cognate word (such as North Frisian skeft "division, stratum," skaft "one of successive parties of workmen"). Similar double senses of "division" and "relay of workers" is in Swedish skift, German schicht.