supplement

Noun

• a supplementary component that improves capability

• a quantity added (e.g. to make up for a deficiency)

• textual matter that is added onto a publication; usually at the end

Verb

• add to the very end
  • He appended a glossary to his novel where he used an invented language
    

• serve as a supplement to
  • Vitamins supplemented his meager diet
    

• add as a supplement to what seems insufficient
  • supplement your diet
    

Related words

• Synonyms: 
  accessory , appurtenance , add-on , supplementation , addendum , postscript , append , add on , affix