identic vs indistinguishable

identic

indistinguishable

noun
  • Any of a set of things that cannot be distinguished. 

adj
  • Not capable of being perceived or known. 

  • Not distinguishable; not capable of being perceived, known, or discriminated as separate and distinct 

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