[n] a supplementary component
[n] a quantity added (e.g. to make up for a deficiency)
[n] textual matter that is added onto a publication; usually at the end
[v] add to the very end; "He appended a glossary to his novel where he used an invented language"
[v] add as a supplement to what seems insufficient; "supplement your diet"
[v] serve as a supplement to; "Vitamins supplemented his meager diet"