major power vs hegemon

major power and hegemon both are nouns.

Word	Noun	Adjective	Verb	Adverb
major power	Yes	No	No	No
hegemon	Yes	No	No	No

As nouns, hegemon is a hyponym of major power; that is, hegemon is a word with a more specific, narrower meaning than major power:

major power: a state powerful enough to influence events throughout the world
hegemon: a leading or paramount power

major power (noun)	hegemon (noun)
a state powerful enough to influence events throughout the world	a leading or paramount power