fraternity house vs frat house

fraternity house and frat house both are nouns.

Word	Noun	Adjective	Verb	Adverb
fraternity house	Yes	No	No	No
frat house	Yes	No	No	No

As nouns, fraternity house and frat house are synonyms defined as:

fraternity house and frat house: a house used as a residence by a chapter of a fraternity

Other synonyms of fraternity house include chapterhouse.

fraternity house (noun)	frat house (noun)
a house used as a residence by a chapter of a fraternity	a house used as a residence by a chapter of a fraternity