gainfulness vs incumbency

gainfulness

noun
  • The state or quality of being gainful; profitableness. 

incumbency

noun
  • Benefice, lucrative position or possession. 

  • A tenure. 

  • The state of being incumbent. 

  • An obligation or duty. 

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