addition vs annexe

addition and annexe both are nouns.

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

As nouns, annexe is a hyponym of addition; that is, annexe is a word with a more specific, narrower meaning than addition:

Other hyponyms of addition include additive, afterthought, annex, extension, wing, attachment, elongation, extension.

addition (noun)	annexe (noun)
the arithmetic operation of summing; calculating the sum of two or more numbers	an addition that extends a main building
the act of adding one thing to another
a component that is added to something to improve it
a suburban area laid out in streets and lots for a future residential area
something added to what you already have
a quantity that is added