supplement in WordNet English dictionary

1. a supplementary component that improves capability
   accessory  appurtenance  supplement  add-on 
   
2. textual matter that is added onto a publication; usually at the end
   addendum  supplement  postscript 
   
3. a quantity added (e.g. to make up for a deficiency)
   supplement  supplementation 
   

1. add to the very end
   "He appended a glossary to his novel where he used an invented language"
   append  add on  supplement  affix 
   
2. add as a supplement to what seems insufficient
   "supplement your diet"
   supplement 
   
3. serve as a supplement to
   "Vitamins supplemented his meager diet"
   supplement