onrush vs onset

onrush

noun
  • A forceful rush or flow forward. 

  • An aggressive assault. 

verb
  • To assault aggressively. 

  • To rush or flow forward forcefully. 

onset

noun
  • A setting about; a beginning. 

  • The initial portion of a syllable, preceding the syllable nucleus. 

  • The beginning of a musical note or other sound, in which the amplitude rises from zero to an initial peak. 

  • The initial phase of a disease or condition, in which symptoms first become apparent. 

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