apartment building vs apartment house

apartment building and apartment house both are nouns.

Word	Noun	Adjective	Verb	Adverb
apartment building	Yes	No	No	No
apartment house	Yes	No	No	No

As nouns, apartment building and apartment house are synonyms defined as:

apartment building and apartment house: a building that is divided into apartments

apartment building (noun)	apartment house (noun)
a building that is divided into apartments	a building that is divided into apartments