indecipherable vs irresolvable

indecipherable

adj
  • Not decipherable; impossible to decode, read, understand or comprehend. 

  • Indistinguishable 

irresolvable

adj
  • Impossible to resolve; insoluble. 

  • Impossible to separate into its component parts. 

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