boardinghouse vs boarding house

boardinghouse and boarding house both are nouns.

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

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

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

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