building vs annexe

building and annexe both are nouns.

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

building (noun)	annexe (noun)
the act of constructing something	an addition that extends a main building
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