cavil vs protestation

cavil

noun
  • A petty or trivial objection or criticism. 

verb
  • To criticise for petty or frivolous reasons. 

protestation

noun
  • a formal solemn objection or other declaration 

  • A declaration in common-law pleading, by which the party interposes an oblique allegation or denial of some fact, protesting that it does or does not exist, and at the same time avoiding a direct affirmation or denial. 

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