addition vs attachment

addition and attachment both are nouns.

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

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

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

addition (noun)	attachment (noun)
the arithmetic operation of summing; calculating the sum of two or more numbers	the act of fastening things together
the act of adding one thing to another	the act of attaching or affixing something
a component that is added to something to improve it	faithful support for a cause or political party or religion
a suburban area laid out in streets and lots for a future residential area	a supplementary part or accessory
something added to what you already have	a connection that fastens things together
a quantity that is added	a writ authorizing the seizure of property that may be needed for the payment of a judgment in a judicial proceeding
	a feeling of affection for a person or an institution