erstwhile vs ex

erstwhile

adj
  • Former, previous. 

  • Respected, honourable. 

ex

adj
  • Ex-, former, previously but no longer. 

  • expensive, dear 

  • the place the train originated from or called at prior to the present location. 

noun
  • A former partner or spouse, usually short for ex-girlfriend, ex-boyfriend, ex-wife or ex-husband. 

  • The name of the Latin-script letter X. 

verb
  • To delete; to cross out 

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