accreditation vs corroboration

accreditation

noun
  • The giving of credentials. 

  • The granting of approval to an institution of higher learning by an official review board after the school has met certain requirements. 

  • The act of accrediting. 

corroboration

noun
  • The act of corroborating, strengthening, or confirming; addition of strength; confirmation 

  • That which corroborates. 

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