incessant vs tenacious

incessant

adj
  • Without pause or stop; not ending, especially to the point of annoyance. 

tenacious

adj
  • Unwilling to yield or give up; dogged. 

  • Having a good memory; retentive. 

  • Holding together; cohesive. 

  • Clinging to an object or surface; adhesive. 

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