whatsoever vs which

whatsoever

det

  • Whatever. 

adv

  • In any way; at all; whatever. 

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. 

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