onrush vs onslaught

onrush

noun
  • An aggressive assault. 

  • A forceful rush or flow forward. 

verb
  • To assault aggressively. 

  • To rush or flow forward forcefully. 

onslaught

noun
  • A fierce attack. 

  • A large number of people or things resembling an attack. 

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