erstwhile vs previous

erstwhile

adj
  • Former, previous. 

  • Respected, honourable. 

previous

adj
  • Prior; occurring before something else, either in time or order. 

  • Premature; acting or occurring too soon. 

noun
  • An existing criminal record (short for "previous convictions") 

  • A track record of similar behaviour. 

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