append
add on
supplement
affix
add to the very end
He appended a glossary to his novel where he used an invented language
add as a supplement to what seems insufficient
supplement your diet
accessory
appurtenance
add-on
a supplementary component that improves capability
serve as a supplement to
Vitamins supplemented his meager diet
supplementation
a quantity added (e.g. to make up for a deficiency)
addendum
postscript
textual matter that is added onto a publication; usually at the end