daytime vs eve

daytime and eve both are nouns.

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

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

daytime: 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 daytime include afternoon, midafternoon, even, evening, eventide.

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