supplement vs addendum

supplement and addendum both are nouns.

Word	Noun	Adjective	Verb	Adverb
supplement	Yes	No	Yes	No
addendum	Yes	No	No	No

As nouns, supplement and addendum are synonyms defined as:

supplement and addendum: textual matter that is added onto a publication; usually at the end

Other synonyms of supplement include postscript.

supplement (noun)	addendum (noun)
a supplementary component that improves capability	textual matter that is added onto a publication; usually at the end
a quantity added (e.g. to make up for a deficiency)
textual matter that is added onto a publication; usually at the end

supplement (verb)	addendum (verb)
add to the very end
add as a supplement to what seems insufficient
serve as a supplement to