day vs morrow

day and morrow both are nouns.

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

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

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

day (noun)	morrow (noun)
a period of opportunity	the next day
time for Earth to make a complete rotation on its axis
a day assigned to a particular purpose or observance
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