one and the same vs synonymous

one and the same

noun
  • The same person or thing. Used to emphasize the identity or equivalence of two things. 

det
  • The same person or thing. Used to emphasize the identity or equivalence of two things. 

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 one and the same and synonymous occurred in a corpus of books? (source: Google Ngram Viewer )