reunion vs party

reunion and party both are nouns.

Word	Noun	Adjective	Verb	Adverb
reunion	Yes	No	No	No
party	Yes	No	Yes	No

As nouns, party is a hypernym of reunion; that is, party is a word with a broader meaning than reunion:

reunion (noun)	party (noun)
the act of coming together again	an occasion on which people can assemble for social interaction and entertainment
a party of former associates who have come together again	a gathering of people for pleasure
	an organization to gain political power
	a band of people associated temporarily in some activity
	a person involved in legal proceedings

reunion (verb)	party (verb)
	have or participate in a party