undue vs unpermissible

undue

adj
  • Not owing or payable. 

  • That which ought not to be done; illegal; unjustified. 

  • Excessive; going beyond that what is natural or sufficient. 

unpermissible

adj
  • Not permissible. 

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