onfall vs set on

onfall

verb
  • To assault, attack. 

  • To fall on or upon. 

noun
  • The fall of the evening. 

  • A fall of rain or snow. 

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

set on

verb
  • To attack. 

  • To be determined to do or achieve something. 

  • To encourage someone, or an animal, to attack someone. 

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