Nouns

(n)addendum, supplement, postscripttextual matter that is added onto a publication; usually at the end
(n)supplement, supplementationa quantity added (e.g. to make up for a deficiency)
(n)accessory, appurtenance, supplement, add-ona supplementary component that improves capability

Verbs

(v)supplementadd as a supplement to what seems insufficient“supplement your diet”
(v)supplementserve as a supplement to“Vitamins supplemented his meager diet”
(v)append, add on, supplement, affixadd to the very end“He appended a glossary to his novel where he used an invented language”