averment vs corroboration

averment

noun
  • verification; establishment by evidence. 

  • The act of averring, or that which is averred; positive assertion. 

  • A positive statement of facts; an allegation; an offer to justify or prove what is alleged. 

corroboration

noun
  • That which corroborates. 

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

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