unwelcome guest vs interloper

unwelcome guest and interloper both are nouns.

Word	Noun	Adjective	Verb	Adverb
unwelcome guest	Yes	No	No	No
interloper	Yes	No	No	No

As nouns, interloper is a hypernym of unwelcome guest; that is, interloper is a word with a broader meaning than unwelcome guest:

unwelcome guest: someone who gets in (to a party) without an invitation or without paying
interloper: someone who intrudes on the privacy or property of another without permission

Other hypernyms of unwelcome guest include intruder, trespasser.

unwelcome guest (noun)	interloper (noun)
someone who gets in (to a party) without an invitation or without paying	someone who intrudes on the privacy or property of another without permission