accede vs nullify

accede

verb
  • To become a party to an agreement or a treaty. 

  • To agree or assent to a proposal or a view; to give way. 

  • To come to an office, state or dignity; to attain, assume (a position). 

nullify

verb
  • To prevent from happening. 

  • To make of no use or value; to cancel out. 

  • To make legally invalid. 

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