which vs whichever

which

det
  • The/Any ... that; whichever. 

  • What, of those mentioned or implied. 

  • Designates the one(s) previously mentioned. 

pron
  • What one or ones (of those mentioned or implied). 

  • The/Any ones that; whichever. 

  • Introduces a relative clause giving further information about something previously mentioned. 

whichever

det
  • Any or either ... that; the ... that. 

  • According to or depending upon which. 

  • Regardless of the ... that; no matter which. 

  • Which ever; emphatic form of 'which'. 

pron
  • Which ever; emphatic form of 'which'. 

  • Irrespective of the one(s) that; no matter which one(s). 

  • Any or either one(s). 

  • According to or depending upon which one(s). 

  • Any or either one(s) that; the one(s) that. 

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