nightyoudaoicibaDictgodict[night 词源字典]
night: [OE] Night is the English member of an ancient Indo-European family of ‘night’-words, represented in virtually all the modern European languages. The ancestral form was *nokt-, and from this have come Greek núx, Latin nox (source of English nocturnal [15] and nocturne [19], and forerunner of French nuit, Italian notte, and Spanish noche), Welsh nos, Latvian nakts, and Russian noch’. The Germanic descendant of *nokt- was *nakht-, source of modern German and Dutch nacht, Swedish natt, Danish nat, and English night. The only exception to the general European picture is modern Irish oidhche ‘night’, a word of unknown origin.
=> nocturnal[night etymology, night origin, 英语词源]
night (n.)youdaoicibaDictgodict
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- (cognates: 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" (cognates: 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]
Compare 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. The Greeks, by contrast, counted their days by mornings.

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.