flatly vs verifiably

flatly

adv
  • In a definite manner; in a manner showing complete certainty. 

  • In a physically flat or level manner. 

  • In a manner that shows no emotion. 

verifiably

adv
  • In a verifiable manner. 

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