sunset vs sundown

sunset and sundown both are nouns.

Word	Noun	Adjective	Verb	Adverb
sunset	Yes	Yes	No	No
sundown	Yes	No	No	No

As nouns, sunset and sundown are synonyms defined as:

sunset and sundown: the time in the evening at which the sun begins to fall below the horizon

sunset (noun)	sundown (noun)
the daily event of the sun sinking below the horizon	the time in the evening at which the sun begins to fall below the horizon
atmospheric phenomena accompanying the daily disappearance of the sun
the time in the evening at which the sun begins to fall below the horizon

sunset (adjective)	sundown (adjective)
providing for termination
of a declining industry or technology