selfsame vs synonymous

selfsame

adj
  • Chiefly preceded by the: precisely the same; the very same; the same not only in being similar but in being identical. 

synonymous

adj
  • Having an identical meaning. 

  • Having a similar meaning. 

  • Such that both its forms yield the same sequenced protein. 

  • Of, or being a synonym. 

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