onrush vs skirmish

onrush

verb
  • To assault aggressively. 

  • To rush or flow forward forcefully. 

noun
  • An aggressive assault. 

  • A forceful rush or flow forward. 

skirmish

verb
  • To engage in a minor battle or dispute 

noun
  • A brief battle between small groups, usually part of a longer or larger battle or war. 

  • Any minor dispute. 

  • A type of outdoor military style game using paintball or similar weapons. 

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