metonym vs synonymum

metonym

noun
  • A word that names an object from a single characteristic of it or of a closely related object; a word used in metonymy. 

  • A concept, idea, or word used to represent, typify, or stand in for a broader set of ideas. 

synonymum

noun
  • Synonym. 

How often have the words metonym and synonymum occurred in a corpus of books? (source: Google Ngram Viewer )