incessant vs ongoing

incessant

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

ongoing

adj
  • Continuing, permanent, lasting. 

  • Presently or currently happening; being in progress. 

noun
  • Something that is going on; a happening. 

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