intermittent vs relentless

intermittent

adj
  • Stopping and starting, occurring, or presenting at intervals; coming after a particular time span. 

  • Existing only for certain seasons; that is, being dry for part of the year. 

relentless

adj
  • Unremitting, steady and persistent. 

  • Unrelenting or unyielding in severity. 

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