day vs eve

day and eve both are nouns.

Word	Noun	Adjective	Verb	Adverb
day	Yes	No	No	No
eve	Yes	No	No	No

As nouns, eve is a hyponym of day; that is, eve is a word with a more specific, narrower meaning than day:

Other hyponyms of day include tomorrow, today, yesterday, morrow, date, day of the month, date, snow day.

As nouns, eve is a hyponym of day; that is, eve is a word with a more specific, narrower meaning than day:

day: the time after sunrise and before sunset while it is light outside
eve: the latter part of the day (the period of decreasing daylight from late afternoon until nightfall)

Other hyponyms of day include afternoon, midafternoon, even, evening, eventide.

day (noun)	eve (noun)
a period of opportunity	the latter part of the day (the period of decreasing daylight from late afternoon until nightfall)
time for Earth to make a complete rotation on its axis	the day before
a day assigned to a particular purpose or observance	the period immediately before something
the time after sunrise and before sunset while it is light outside
a point or period in time
the recurring hours when you are not sleeping (especially those when you are working)
an era of existence or influence
the time for one complete rotation of the earth relative to a particular star, about 4 minutes shorter than a mean solar day
the period of time taken by a particular planet (e.g. Mars) to make a complete rotation on its axis