party vs stag party

party and stag party both are nouns.

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

As nouns, stag party is a hyponym of party; that is, stag party is a word with a more specific, narrower meaning than party:

party (noun)	stag party (noun)
an occasion on which people can assemble for social interaction and entertainment	a party for men only (or one considered suitable for men only)
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

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