twenty-four hours vs hour

twenty-four hours and hour both are nouns.

Word	Noun	Adjective	Verb	Adverb
twenty-four hours	Yes	No	No	No
hour	Yes	No	No	No

twenty-four hours (noun)	hour (noun)
time for Earth to make a complete rotation on its axis	distance measured by the time taken to cover it
	a period of time equal to 1/24th of a day
	clock time
	a special and memorable period