boarding house vs boardinghouse

boarding house and boardinghouse both are nouns.

Word	Noun	Adjective	Verb	Adverb
boarding house	Yes	No	No	No
boardinghouse	Yes	No	No	No

As nouns, boarding house and boardinghouse are synonyms defined as:

boarding house and boardinghouse: a private house that provides accommodations and meals for paying guests

boarding house (noun)	boardinghouse (noun)
a private house that provides accommodations and meals for paying guests	a private house that provides accommodations and meals for paying guests