nightspot (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.

c. 1200, "moral stain," probably from Old English splott "a spot, blot, patch (of land)," and partly from or related to Middle Dutch spotte "spot, speck." Other cognates are East Frisian spot "speck," North Frisian spot "speck, piece of ground," Old Norse spotti "small piece," Norwegian spot "spot, small piece of land." It is likely that some of these are borrowed from others, but the exact evolution now is impossible to trace.

Meaning "speck, stain" is from mid-14c. The sense of "particular place, small extent of space" is from c. 1300. Meaning "short interval in a broadcast for an advertisement or announcement" is from 1923. Preceded by a number (as in five-spot) it originally was a term for "prison sentence" of that many years (1901, American English slang). To put (someone) on the spot "place in a difficult situation" is from 1928. Colloquial phrase hit the spot "satisfy, be what is required" is from 1868. Spot check is attested by 1933. Adverbial phrase spot on "completely right" attested from 1920.