certainly vs certifiably

certainly

adv
  • Without doubt, surely. 

  • In a way which is certain; with certainty. 

  • An emphatic affirmative answer; of course. 

certifiably

adv
  • Undoubtedly, demonstrably. 

  • With the potential for certification. 

  • To a great extent. 

  • Genuinely 

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