onrush vs outbreak

onrush

noun
  • An aggressive assault. 

  • A forceful rush or flow forward. 

verb
  • To assault aggressively. 

  • To rush or flow forward forcefully. 

outbreak

noun
  • An outburst or sudden eruption, especially of violence and mischief. 

  • An eruption; the sudden appearance of a rash, disease, etc. 

  • Synonym of breakout (“escape from prison”) 

  • A sudden increase. 

verb
  • To burst out or break forth. 

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