undue vs unfair

undue

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

  • Not owing or payable. 

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

unfair

adj
  • not fair, unjust 

  • sorrowful; sad 

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