apartment building vs building

apartment building and building both are nouns.

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

As nouns, building is a hypernym of apartment building; that is, building is a word with a broader meaning than apartment building:

apartment building: a building that is divided into apartments
building: a structure that has a roof and walls and stands more or less permanently in one place

Other hypernyms of apartment building include edifice.

apartment building (noun)	building (noun)
a building that is divided into apartments	the act of constructing something
	the commercial activity involved in repairing old structures or constructing new ones
	a structure that has a roof and walls and stands more or less permanently in one place
	the occupants of a building