Synonyms for Supplement (same or very similar meaning)
WordNet sense 1 (textual matter that is added onto a publication; usually at the end):
addendum, postscript
WordNet sense 2 (a quantity added (e.g. to make up for a deficiency)):
supplementation
WordNet sense 3 (a supplementary component that improves capability):
accessory, add-on, appurtenance
WordNet sense 4 (add to the very end):
affix, append, affix, add on
From the ODE community, based on WordNet
add/edit