crasher vs unwelcome guest

crasher and unwelcome guest both are nouns.

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

As nouns, crasher and unwelcome guest are synonyms defined as:

crasher and unwelcome guest: someone who gets in (to a party) without an invitation or without paying

Other synonyms of crasher include gatecrasher.

crasher (noun)	unwelcome guest (noun)
someone who gets in (to a party) without an invitation or without paying	someone who gets in (to a party) without an invitation or without paying