onset vs outbreak

onset

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

  • 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. 

  • A setting about; a beginning. 

outbreak

noun
  • An eruption; the sudden appearance of a rash, disease, etc. 

  • Synonym of breakout (“escape from prison”) 

  • An outburst or sudden eruption, especially of violence and mischief. 

  • A sudden increase. 

verb
  • To burst out or break forth. 

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