night

Old English niht (West Saxon neaht, Anglian næht, neht) "night, darkness;" the vowel indicating that the modern word derives from oblique cases (genitive nihte, dative niht), from Proto-Germanic *nakht- (cf. 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" (cf. Greek nuks "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 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]

Cf. German Weihnachten "Christmas." 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.

To work nights preserves the Old English genitive of time. Night shift is attested from 1710 in the sense of "garment worn by a woman at night" (see shift (n.1)); meaning "gang of workers employed after dark" is from 1839. Night soil "excrement" (1770) is so called because it was removed (from cesspools, etc.) after dark. Night train attested from 1838. Night life "habitual nocturnal carousing" attested from 1852.

Also day and night. Continually, without stopping. This phrase is used either literally, as in The alarm is on night and day, or hyperbolically, as in We were working day and night on these drawings. Shakespeare put it by night and day in The Comedy of Errors (4:2): “Time comes stealing on by night and day.”

In addition to the idioms beginning with night

• night and day
• night owl

also see:

• black as night
• call it a day (night)
• dead of (night)
• different as night and day
• good night
• make a day (night) of it
• ships that pass in the night