dust up vs onfall

dust up

verb
  • To attack (a person) physically; to beat up. 

  • To cover with dust. 

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. 

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