world power vs nation

world power and nation both are nouns.

Word	Noun	Adjective	Verb	Adverb
world power	Yes	No	No	No
nation	Yes	No	No	No

As nouns, nation is a hypernym of world power; that is, nation is a word with a broader meaning than world power:

world power: a state powerful enough to influence events throughout the world
nation: a politically organized body of people under a single government

Other hypernyms of world power include body politic, commonwealth, country, land, res publica, state.

world power (noun)	nation (noun)
a state powerful enough to influence events throughout the world	a politically organized body of people under a single government
	the people who live in a nation or country
	a federation of tribes (especially Native American tribes)