demerit vs infirmity

demerit

noun
  • A quality of being inadequate; a fault; a disadvantage 

  • A mark given for bad conduct to a person attending an educational institution or serving in the army. 

  • That which one merits or deserves, either of good or ill; desert. 

infirmity

noun
  • a moral weakness or defect 

  • feebleness, frailty or ailment, especially due to old age. 

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