day vs hour

day and hour both are nouns.

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

day (noun)	hour (noun)
a period of opportunity	distance measured by the time taken to cover it
time for Earth to make a complete rotation on its axis	a period of time equal to 1/24th of a day
a day assigned to a particular purpose or observance	clock time
the time after sunrise and before sunset while it is light outside	a special and memorable period
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