nightfall(n = noun.time) crepuscle, crepuscule, dusk, evenfall, fall, gloam, gloaming, twilight - the time of day immediately following sunset; "he loved the twilight"; "they finished before the fall of night"
is a kind of hour, time of day
is a part of eve, even, evening, eventide
has particulars: night

   The close of the day; the arrival of the night; the period at and just after dusk. Swift. [1913 Webster]

nightfall, n. the onset of night; the end of daylight.

N  evening, eve, decline of day, fall of day, close of day, candlelight, candlelighting, eventide, nightfall, curfew, dusk, twilight, eleventh hour, sunset, sundown, going down of the sun, cock-shut, dewy eve, gloaming, bedtime, afternoon, postmeridian, p, m, autumn, fall, fall of the leaf, autumnal equinox, Indian summer, St. Luke's summer, St. Martin's summer, midnight, dead of night, witching hour, witching hour of night, witching time of night, winter, killing time, vespertine, autumnal, nocturnal, midnight, the outpost of advancing day, sable-vested Night, this gorgeous arch with golden worlds inlay'd.