nightfall vs twilight

nightfall and twilight both are nouns.

Word	Noun	Adjective	Verb	Adverb
nightfall	Yes	No	No	No
twilight	Yes	Yes	No	No

As nouns, nightfall and twilight are synonyms defined as:

Other synonyms of nightfall include crepuscle, crepuscule, dusk, evenfall, fall, gloam, gloaming.

nightfall (noun)	twilight (noun)
the time of day immediately following sunset	the diffused light from the sky when the sun is below the horizon but its rays are refracted by the atmosphere of the earth
	a condition of decline following successes
	the time of day immediately following sunset

nightfall (adjective)	twilight (adjective)
	lighted by or as if by twilight