1.  That part of the natural day when the sun is beneath the horizon, or the time from sunset to sunrise; esp., the time between dusk and dawn, when there is no light of the sun, but only moonlight, starlight, or artificial light. [1913 Webster]
"And God called the light Day, and the darkness he called Night." [1913 Webster]

2.  Darkness; obscurity; concealment. [1913 Webster]
" Night is sometimes used, esp. with participles, in the formation of self-explaining compounds; as, night-blooming, night-born, night-warbling, etc." [1913 Webster]
"Nature and nature's laws lay hid in night." [1913 Webster]
"She closed her eyes in everlasting night." [1913 Webster]
"Do not go gentle into that good night
Rage, rage against the dying of the light." [PJC]
"So help me God, as I have watched the night,
Ay, night by night, in studying good for England." [1913 Webster]

night, n.
1 the period of darkness between one day and the next; the time from sunset to sunrise.
2 nightfall (shall not reach home before night).
3 the darkness of night (as black as night).
4 a night or evening appointed for some activity, or spent or regarded in a certain way (last night of the Proms; a great night out).

Idiom:
night-blindness = NYCTALOPIA. night fighter an aeroplane used for interception at night. night-hawk
1 a nocturnal prowler, esp. a thief.
2 a nightjar. night-life entertainment available at night in a town. night-light a dim light kept on in a bedroom at night. night-long throughout the night. night nurse a nurse on duty during the night. night-owl colloq. a person active at night. night safe a safe with access from the outer wall of a bank for the deposit of money etc. when the bank is closed. night school an institution providing evening classes for those working by day. night shift a shift of workers employed during the night. night-soil the contents of cesspools etc. removed at night, esp. for use as manure. night-time the time of darkness.
night-watchman
1 a person whose job is to keep watch by night.
2 Cricket an inferior batsman sent in when a wicket falls near the close of a day's play.

Derivative:
nightless adj.

Etymology:
OE neaht, niht f. Gmc

N  darkness, absence of light, blackness, obscurity, gloom, murk, dusk, Cimmerian darkness, Stygian darkness, Egyptian darkness, night, midnight, dead of night, witching hour of night, witching time of night, blind man's holiday, darkness visible, darkness that can be felt, palpable obscure, Erebus, the jaws of darkness, sablevested night, shade, shadow, umbra, penumbra, sciagraphy, obscuration, occultation, adumbration, obumbration, obtenebration, offuscation, caligation, extinction, eclipse, total eclipse, gathering of the clouds, shading, distribution of shade, chiaroscuro, noctivagation, black body, hohlraum, black hole, dark star, dark matter, cold dark matter, dark, darksome, darkling, obscure, tenebrious, sombrous, pitch dark, pitchy, pitch black, caliginous, black, sunless, lightless &c (sun) (light), somber, dusky, unilluminated &c (illuminate), nocturnal, dingy, lurid, gloomy, murky, murksome, shady, umbrageous, overcast, cloudy, darkened, dark as pitch, dark as a pit, dark as Erebus, benighted, noctivagant, noctivagous, in the dark, in the shade, brief as the lightning in the collied night, eldest Night and Chaos, ancestors of Nature, the blackness of the noonday night, the prayer of Ajax was for light.

bird of night, black-crowned night heron, bonfire night, dead of night, every night, good night, guest night, guy fawkes night, midsummer night, night and day, night before christmas, night bell, night bird, night blindness, night court, night game, night heron, night jasmine, night jessamine, night latch, night letter, night lettergram, night life, night lizard, night owl, night porter, night raven, night rider, night school, night shift, night snake, night soil, night spot, night terror, night terrors, night vision, night watch, night watchman, opening night, queen of the night, saturday night special, st john's night, this night, twelfth night, very night signals, very's night signals, walpurgis night, watch night, wedding night, yellow-crowned night heron