onfall vs outbreak

onfall

verb
  • To fall on or upon. 

  • To assault, attack. 

noun
  • The fall of the evening. 

  • A fall of rain or snow. 

  • A falling on or upon; an attack, onset, or assault. 

outbreak

verb
  • To burst out or break forth. 

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

  • Synonym of breakout (“escape from prison”) 

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

  • A sudden increase. 

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