dusk vs nightfall

dusk and nightfall both are nouns.

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

As nouns, dusk and nightfall are synonyms defined as:

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

dusk (noun)	nightfall (noun)
the time of day immediately following sunset	the time of day immediately following sunset

dusk (verb)	nightfall (verb)
become dusk