counterpart vs synonym

counterpart

noun
  • One who or that which resembles another. 

  • Either of two parts that fit together, or complement one another. 

  • A duplicate of a legal document. 

  • One who or that which has corresponding functions or characteristics. 

  • Either half of a flattened fossil when the rock has split along the plane of the fossil. 

verb
  • To counterbalance. 

synonym

noun
  • A word whose meaning is the same as that of another word. 

  • An alternative (often shorter) name defined for an object in a database. 

  • Any name for a taxon, usually a validly published, formally accepted one, but often also an unpublished name. 

  • A word or phrase with a meaning that is the same as, or very similar to, another word or phrase. 

  • Any of the formal names for a taxon, including the valid name (i.e. the senior synonym). 

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