employ vs incumbency

employ

noun
  • The state of being an employee; employment. 

verb
  • To hire (somebody for work or a job). 

  • To use (somebody for a job, or something for a task). 

  • To make busy. 

incumbency

noun
  • A tenure. 

  • Benefice, lucrative position or possession. 

  • The state of being incumbent. 

  • An obligation or duty. 

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