evening vs eventide

evening and eventide both are nouns.

Word	Noun	Adjective	Verb	Adverb
evening	Yes	No	No	No
eventide	Yes	No	No	No

As nouns, evening and eventide are synonyms defined as:

evening and eventide: the latter part of the day (the period of decreasing daylight from late afternoon until nightfall)

Other synonyms of evening include eve, even.

evening (noun)	eventide (noun)
the latter part of the day (the period of decreasing daylight from late afternoon until nightfall)	the latter part of the day (the period of decreasing daylight from late afternoon until nightfall)
a later concluding time period
the early part of night (from dinner until bedtime) spent in a special way